Beam projecting device

ABSTRACT

A beam projecting apparatus includes a light source that emits a laser beam and a colliminating lens that renders the emitted laser beam a substantially parallel beam. A beam projecting device includes a beam projecting portion from which the laser beam is projected outwardly so that the laser beam has a beam waist located at a predetermined position spaced from the beam projecting apparatus. The beam projecting apparatus further includes a system that detects a curvature of wavefront of the substantially parallel beam at the predetermined position.

This is a divisional of application Ser. No. 08/562,827, filed Nov. 27,1995, the contents of which are herein incorporated by reference in itsentirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a beam projecting device for forming areference plane by projecting a light beam, such as a laser beam, whilerotating a light beam projecting portion of the beam projecting device.

2. Description of Related Art

A known example of the type of device mentioned above is a lasersurveying device or so called "laser planer". In this device a rotatingmember projects a laser beam emitted by a laser light source in,approximately, a horizontal direction toward an object to be surveyed,which is then scanned so as to form a reference plane. In this case aheight of a laser beam spot against the object to be surveyed can beeither visually observed through the eye or through the use of adetector. This type of laser surveying device is known (refer toUnexamined Japanese Patent Publication No. 5-322564).

Known laser surveying devices are mostly used for forming a referenceplane in a wide distance range, from a short distance (e.g. 0.5 m-1.5 m)to a long distance (e.g. 100 m-200 m). In this case, simple focusing isdesired, and detection sensitivity should be prevented from varying whena beam position is detected by a detector. Also it is desirable that abeam detector can precisely detect a position of a laser beam, emittedby a laser surveying device, and that the projected laser beam isclearly visible to the naked eye.

Since laser surveying devices are often used outdoors in extremeconditions (e.g. -20° C. to +50° C.) the focal point may deviate due toan expansion or contraction of a lens and/or a lens supporting framecaused by a variation in temperature.

Normally, variations in temperature cause the beam waist position toshift due to an expansion or contraction of the lens supporting frame,variations in the refractive index of a lens itself, the variation of anoscillation wavelength of a laser light source, etc.

FIGS. 68 and 69 are graphs showing the relationship between a projectingdistance of a laser beam and a beam diameter at a constant temperature.In FIG. 68, the initial projecting beam diameter W is 8 mm. In FIG. 69,the initial projecting beam diameter W is 12.5 mm. In both cases, thewavelength of laser beams is the same, and symbol "x" in each figureindicates a beam waist position.

It is understood that when the beam waist position x varies, the beamdiameter varies at each distance in both figures. For example, in FIG.69, when the laser surveying device is used at a close distance range,ranging from about 10 m to 70 m, the beam waist position x should be setat 50.879 m. On the other hand, when the device is used for a longdistance range, ranging from about 100 m to 200 m, the beam waistposition x should be set at 97.505 m.

FIGS. 66 and 67 are graphs showing variations in beam diameters atdifferent projecting distances while using the variation in temperatureas a parameter. In these figures the diameter of a laser beam atdifferent projecting distances is plotted under the condition that alaser surveying device is provided with a lens system for making aparallel beam of an adequate size and where the diameter of the laserbeam at the projecting end of the device (i.e. initial projecting beamdiameter), and a predetermined beam waist position X (i.e. a distancefrom the projecting end of the device to a position where the beam waistis formed) are given. In FIGS. 66 and 67, the initial projecting beamdiameters W are 8 mm and 12.5 mm, respectively.

FIG. 66 shows that when the temperature is varied from -20° C. to +50°C., the variation of the diameter of a laser beam at differentprojecting distances for a laser surveying device having a projectingbeam wavefront with a radius of curvature R of 78 m, under the conditionthat the beam waist position X is initially set at 39.578 m at atemperature of 20° C., that is, the distance from the projecting end ofthe device to the position at which the beam waist is formed is 39.578m.

Likewise, FIG. 67 shows that when the temperature is varied from -20° C.to +50° C., the variation of the diameter of a laser beam at differentprojecting distances for a laser surveying device having a projectingbeam wave front with a radius of curvature R of 190 m, under thecondition that the beam waist position X is initially set at 96.605 m ata temperature of 20° C., that is, the distance from the projecting endof the device to the position at which the beam waist is formed is96.605 m.

As can be understood from FIGS. 66 and 67 even if an initial projectingbeam diameter, a beam waist diameter, and a beam waist position areadequately determined initially, the beam waist position X varies due tovariations in temperature and the beam diameters are not equal at eachbeam waist position X at different temperatures.

When a semiconductor laser is used as a light source, since it providesa diverging laser beam, a collimating lens is used to obtain anapproximately parallel laser beam. Transverse magnification of theoptical system of the laser projecting device is given as the ratio ofthe numerical aperture of an incident side of a laser beam from thesemiconductor laser, to the numerical aperture of an outgoing sidethereof. When it is desired to effectively utilize a laser beam of thesemiconductor laser, since the numerical aperture of the incident sideof the collimating lens should be approximately 0.2-0.4, and thenumerical aperture of the emitting side of the collimating lens shouldbe approximately 0.00002-0.0005, a magnifying and projecting system witha very large magnifying power thus needs to be constructed.

Since a laser beam with the above mentioned large magnifying power isprojected from the laser surveying device, a slight variation to thelaser beam in the laser surveying device causes quite a large variationto the laser beam when it is projected from the laser surveying device.This variation increases over distance. Therefore, in a conventionallaser surveying device, the following problems may occur: a convergingpoint is greatly deviated from a designed position; the beam diameterbecomes too large at a distance far away from the device so as not to beprecisely detected by the laser detector; and the luminance required forvisual observation is insufficient, which causes the problem of onlyhaving a short usable distance, when a long distance may be required.

In order to solve the problem described above, in the U.S. Pat. No.5,225,928 a lens has been proposed which has an overall index ofrefraction which changes with temperature and wavelength. This change inindex of refrection changes the focal point of the lens for the laserbeam in an amount which substantially compensates for defocusing causedby temperature effects on the mounting length and laser beam wavelength.However, optical glasses used in a collimator are not available toprecisely compensate for all variations in temperature that may occur.Additionally, in the case when a semiconductor laser with a largeradiation angle is used as a light source, a collimating lens with alarge numerical aperture (NA) is required, this makes it much moredifficult to completely compensate for the variations in temperature.

However, since the variation in oscillation wavelength is not always thesame in all semiconductor lasers, and a laser surveying device isdesigned according to a standard semiconductor laser, a desiredperformance may not be expected when the laser surveying device isprovided with certain semiconductor lasers.

Previously, even when a laser surveying device was designed so as tocompletely compensate for variations in temperature, it was quitedifficult in reality to completely eliminate the influence oftemperature variation. The reason for this is because temperaturedistribution occurs in each member constituting the laser projectingdevice, for example, the laser projecting device includes a light sourcesuch as a semiconductor laser and the like, and the light source itselfis a heat source which causes a difference in temperature between thedevice and the outside, which causes a variation in temperature.Further, heat generated by a motor used to rotate a laser beamprojecting portion of the device cannot be neglected. Therefore, even ifa laser surveying device was previously designed, in theory, so as tocompletely compensate for variations in outside temperature, a desiredbeam diameter at a prescribed distance could not be obtained in reality,where various types of temperature change occur.

SUMMARY OF THE INVENTION

The primary object of the present invention is to provide a beamprojecting device in which the beam waist position of a projected lightbeam, which varies due to variations in temperature, is controlled suchthat variations in the beam diameter are minimized.

The second object of the present invention is to provide a beamprojecting device capable of sufficiently transmitting a fine light beamin a wide distance range, ranging from a short distance to a longdistance, even if the light beam is a diverging laser beam.

The third object of the present invention is to provide a laser beamprojecting device in which an optimum or desired beam waist position andbeam waist diameter can be automatically set at a desired distance,further, the set beam waist position and beam diameter can be maintaineddespite temperature variations and wavelength variations. Further,another object of the present invention is to provide a detecting systemfor detecting a projected laser beam waist position, and a laserprojecting device for freely setting a beam waist position in accordancewith a signal outputted from the detecting system.

To achieve the object mentioned above, according to the presentinvention, there is provided a beam projecting.

The beam waist position controlling means maintains the beam waistposition at a predetermined distance from the light projecting means inspite of a temperature variation.

To achieve the object mentioned above, according to the presentinvention, there is provided a beam projecting apparatus comprising: alight source emitting a laser beam; a beam projecting means including abeam projecting portion from which the laser beam is projected outwardlyso that the laser beam has a beam waist at a predetermined positionapart from the beam projecting apparatus; a beam waist positionadjusting optical system disposed along a light path from the lightsource to the beam projecting portion, at least one lens element of thebeam waist position adjusting optical system being movable along anoptical axis thereof; a temperature detecting means for detecting atemperature in the beam projecting apparatus; a control means forcontrolling a movement of the at least one lens element in associationwith the temperature detected by the temperature detecting means so thata deviation of the beam waist position from said predetermined positiondue a temperature change is nullified.

According to another aspect of the present invention, there is provideda beam projecting apparatus comprising: a beam projecting apparatuscomprising: a light source emitting a laser beam; a collimating lens formaking the laser beam a substantially parallel beam; a beam projectingmeans including a beam projecting portion from which the collimatedlaser beam is projected outwardly; a holding member for holding saidcollimating lens, the holding member defining a distance between thelight source and said collimating lens; wherein a change of back focaldistance of said collimating lens due to a temperature changesubstantially corresponds to a change of said distance between the lightsource and the collimating lens caused by an expansion or contraction ofthe holding member due to the temperature change.

According to another aspect of the present invention, there is provideda beam projecting apparatus comprising: a light source emitting a laserbeam; a collimating lens for making the laser beam substantiallyparallel beam; a beam projecting means including a beam projectingportion from which the substantially parallel beam being projectedoutwardly so that the beam has a beam waist position apart from the beamprojecting apparatus; and means for detecting a curvature of wavefrontof said parallel beam at predetermined position.

According to another aspect of the present invention, there is provideda beam projecting apparatus including a light source emitting lightbeams, an automatic adjusting means for correcting an inclination of anoptical axis of the light beams; a collimating lens provided for makingthe light beams from the light source parallel, the collimating lensbeing provided in a lens holding frame; a rotatable beam projectingmeans for projecting the light beam from said apparatus, a rotationalaxis of the rotatable beam projecting means being aligned with theoptical axis of said light beams; a beam waist-forming means for forminga beam waist of the light beams at a predetermined position along theoptical axis of said light beam projected from the rotatable beamprojecting means; and means for controlling total operations of the beamprojecting apparatus, the beam projecting apparatus, comprising: meansfor detecting disturbance, in the disturbance the beam projectingapparatus being exposed to; and means for compensating said disturbancedetected by the disturbance detecting means so that a position of beamwaist, formed by the beam waist forming means, being maintained at apredetermined position along said optical axis of said light beams.

The present disclosure relates to subject matter contained in Japanesepatent application Nos. 06-291379 (filed on Nov. 25, 1994), 06-328790(filed on Dec. 28, 1994) and 07-47450 (filed on Mar. 7, 1995) which areexpressly incorporated herein by reference in their entireties.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described below in detail with reference to theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view of an overall laser surveying deviceaccording to the present invention;

FIG. 2 is an enlarged side view of a beam projecting optical system andsome peripheral members thereof of the laser surveying device shown inFIG. 1;

FIG. 3 is an enlarged plan view of the main components of the lasersurveying device shown in FIG. 1;

FIG. 4 is a side view of a laser diode, a collimating lens and a laserbeam cross-sectional shape conversion optical system of the lasersurveying device shown in FIG. 1;

FIG. 5 is a cross-sectional view of a laser beam projected from thelaser diode of the laser surveying device shown in FIG. 1, whosesectional shape is elliptical;

FIG. 6 is a cross-sectional view of a converted laser beam whosesectional shape has been converted into a substantially round shape bythe laser beam cross-sectional shape conversion optical system of thelaser surveying device shown in FIG. 1;

FIG. 7 is a view illustrating the beam waist position by the beamexpander of the laser surveying device shown in FIG. 1;

FIG. 8 is a view illustrating the correction of the beam waist positionby the beam expander of the laser surveying device shown in FIG. 1;

FIG. 9 is a graph showing the variation of the beam diameter atdifferent projection distances when the amount of shift δ of the frontlens group is a prescribed fixed value, wherein the beam magnificationof the beam expander B is 1.33 according to an embodiment of the presentinvention;

FIG. 10 is a graph showing the variation of the beam diameter atdifferent projection distances when the amount of shift δ of the frontlens group is a prescriber fixed value, wherein the beam magnificationof the beam expander B is 2.08 according to another embodiment of thepresent invention;

FIG. 11 is a graph showing the relationship between the amount of shiftin the front lens group due to temperature, when a beam expander havinga beam magnifying power of 1.33 is used, according to another embodimentof the present invention;

FIG. 12 is a graph showing the relationship between the amount of shiftin the front lens group due to temperature, when a beam expander havinga beam magnifying power of 2.08 is used according to the same embodimentof the present invention, as that shown in FIG. 11;

FIG. 13 is a graph showing variations in beam diameter at differentprojecting distances, due to variations in temperature;

FIG. 14 is another graph showing variations in beam diameter atdifferent projecting distances, due to variations in temperature;

FIG. 15 is a schematic view of a lens arrangement of a first embodimentof a collimating lens system, according to the present invention;

FIG. 16 shows various aberration diagrams in the vertical direction forthe collimating lens system shown in FIG. 15;

FIG. 17 shows aberration diagrams in the horizontal direction for thecollimating lens system shown in FIG. 15;

FIG. 18 shows wavefront aberration diagrams for the collimating lenssystem shown in FIG. 15;

FIG. 19 is a schematic view of a lens arrangement of a beam diameterchanging optical system which is used together with the collimating lenssystem shown in FIG. 15;

FIG. 20 shows various aberration diagrams in the vertical direction forthe beam diameter changing optical system shown in FIG. 19;

FIG. 21 shows aberration diagrams in the horizontal direction for thebeam diameter changing optical system shown in FIG. 19;

FIG. 22 shows wavefront aberration diagrams for the beam diameterchanging optical system shown in FIG. 19;

FIG. 23 is a schematic view of a lens arrangement of a second embodimentof a collimating lens system, according to the present invention;

FIG. 24 shows various aberration diagrams in the vertical direction forthe collimating lens system shown in FIG. 23;

FIG. 25 shows aberration diagrams in the horizontal direction for thecollimating lens system shown in FIG. 23;

FIG. 26 shows wavefront aberration diagrams for the collimating lenssystem shown in FIG. 23;

FIG. 27 is a schematic view of a lens arrangement of a beam diameterchanging optical system which is used together with the collimating lenssystem shown in FIG. 23;

FIG. 28 shows various aberration diagrams in the vertical direction forthe beam diameter changing optical system shown in FIG. 27;

FIG. 29 shows aberration diagrams in the horizontal direction for thebeam diameter changing optical system shown in FIG. 27;

FIG. 30 shows wavefront aberration diagrams for the beam diameterchanging optical system shown in FIG. 27;

FIG. 31 is a schematic view of a lens arrangement of a third embodimentof a collimating lens system, according to the present invention;

FIG. 32 shows various aberration diagrams in the vertical direction forthe collimating lens system shown in FIG. 31;

FIG. 33 shows aberration diagrams in the horizontal direction for thecollimating lens system shown in FIG. 31;

FIG. 34 shows wavefront aberration diagrams for the collimating lenssystem shown in FIG. 31;

FIG. 35 is a schematic view of a lens arrangement of a beam diameterchanging optical system which is used together with the collimating lenssystem shown in FIG. 31;

FIG. 36 shows various aberration diagrams in the vertical direction forthe beam diameter changing optical system shown in FIG. 35;

FIG. 37 shows aberration diagrams in the horizontal direction for thebeam diameter changing optical system shown in FIG. 35;

FIG. 38 shows wavefront aberration diagrams for the beam diameterchanging optical system shown in FIG. 35;

FIG. 39 is a schematic view of a lens arrangement of a fourth embodimentof a collimating lens system, according to the present invention;

FIG. 40 shows various aberration diagrams in the vertical direction forthe collimating lens system shown in FIG. 39;

FIG. 41 shows aberration diagrams in the horizontal direction for thecollimating lens system shown in FIG. 39;

FIG. 42 shows wavefront aberration diagrams for the collimating lenssystem shown in FIG. 39;

FIG. 43 is a schematic view of a lens arrangement of a beam diameterchanging optical system which is used together with the collimating lenssystem shown in FIG. 39;

FIG. 44 shows various aberration diagrams in the vertical direction forthe beam diameter changing optical system shown in FIG. 43;

FIG. 45 shows aberration diagrams in the horizontal direction for thebeam diameter changing optical system shown in FIG. 43;

FIG. 46 shows wavefront aberration diagrams for the beam diameterchanging optical system shown in FIG. 43;

FIG. 47 is a schematic view of a lens arrangement of a fifth embodimentof a collimating lens system, according to the present invention;

FIG. 48 shows various aberration diagrams in the vertical direction forthe collimating lens system shown in FIG. 47;

FIG. 49 shows aberration diagrams in the horizontal direction for thecollimating lens system shown in FIG. 47;

FIG. 50 shows wavefront aberration diagrams for the collimating lenssystem shown in FIG. 47;

FIG. 51 is a schematic view of a lens arrangement of a beam diameterchanging optical system used together with the collimating lens systemshown in FIG. 47;

FIG. 52 shows various aberration diagrams in the vertical direction forthe beam diameter changing optical system shown in FIG. 51;

FIG. 53 shows aberration diagrams in the horizontal direction for thebeam diameter changing optical system shown in FIG. 51;

FIG. 54 shows wavefront aberration diagrams for the beam diameterchanging optical system shown in FIG. 51;

FIG. 55 is a schematic view of a lens arrangement of the collimatinglens system shown in FIG. 23 together with the beam diameter changingoptical system shown in FIG. 27;

FIG. 56 shows various aberration diagrams in the vertical direction forthe whole of the lens system shown in FIG. 55;

FIG. 57 is a graph showing variations in the beam diameter of aprojected laser beam at a distance of 200 m, due to variations intemperature, after the laser beam has been projected through thecollimating lens system shown in FIG. 15 and the beam diameter changingoptical system shown in FIG. 19;

FIG. 58 is a graph showing variations in the beam diameter of aprojected laser beam at a distance of 200 m, due to variations intemperature, after the laser beam has been projected through thecollimating lens system shown in FIG. 23 and the beam diameter changingoptical system shown in FIG. 27;

FIG. 59 is a schematic view of a first embodiment of a beam projectingapparatus to which the present invention is applied;

FIG. 60 illustrates a focus error detecting system applied to the beamprojecting apparatus of the first embodiment shown in FIG. 59;

FIG. 61 is a graph showing focus error signals obtained through thefocus error detecting system in the beam projecting apparatus of thefirst embodiment;

FIG. 62 is a schematic view of a second embodiment of a beam projectingapparatus to which the present invention is applied;

FIG. 63 illustrates a radial shearing interference meter applied to thebeam projecting apparatus of the second embodiment shown in FIG. 62;

FIG. 64 illustrates the relationship between the radius of curvature ofan incident wavefront and the interference fringes observed through theradial shearing interference meter shown in FIG. 63;

FIG. 65 is a schematic view of a beam projecting apparatus of the thirdembodiment to which the present invention is applied;

FIG. 66 is a graph showing variations in beam diameter due to variationsin temperature;

FIG. 67 is another graph showing variations in beam diameter due tovariations in temperature;

FIG. 68 is a graph showing the relationship between the beam waistposition and the beam diameter, when the beam diameter is initially setat 8 mm;

FIG. 69 is a graph showing the relationship between the beam waistposition and the beam diameter, when the beam diameter is initially setat 12.5 mm; and

FIG. 70 is a graph showing the relationship between the radius ofcurvature of a wavefront at the beam projecting point and the beam waistposition.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a cross-sectional view of an overall laser surveying device(i.e. beam projecting device) 11 to which the present invention isapplied. The laser surveying device 11 is provided with a substantiallycylindrical-shaped housing 12 and a projector body 13 placed in thehousing 12. A transparent member 16 formed in the shape of a cylinder isfixed onto the housing 12 at the upper portion of the housing 12. Thetransparent member 16 surrounds a rotatable laser emitter 15 provided atthe top of the projector body 13. A battery case 17 is fixed to thebottom of the laser surveying device 11. The battery case 17accommodates a battery (not shown) used as a power supply for the lasersurveying device 11.

The housing 12 is provided with a substantially inverted conical-shapedsliding guide section 19 at the center of the upper portion of thehousing 12, and a circular hole 12a at the center of the bottom portionof the housing 12. Two circular holes 17a are formed at the center ofthe battery case 17 on the upper and lower walls, respectively, and thecircular hole 12a aligns with the upper circular hole 17a when thebattery case 17 is attached to the bottom of the housing 12 so as toallow a laser beam emitted from inside the housing 12 to proceeddownwards out of the laser surveying device 11 through the circularholes 12a and 17a. Further, the sliding guide section 19 is provided atthe center of the bottom portion thereof with a circular hole 19a. Thediameter of the hole 19a is a size predetermined to be smaller than thediameter of a spherical surface 21a of a bulged part 21.

The projector body 13 is provided with a hollow member 20 having avertically extending inner bore, which extends in the vertical directionas viewed from FIG. 1. The rotatable laser emitter 15 is rotatablysupported through a bearing 10 on the top of the hollow member 20. Thehollow member 20 is provided at the upper portion thereof with thebulged portion 21. The bulged portion 21 is supported in such a way thatthe rotatable laser emitter 15 can be tilted in all directions, relativeto the housing 12, about the center of the curvature of the spheresurface 21a. The rotatable laser emitter 15 can also move freely toadjust a reference plane defined by laser beams L₃ with respect to thehorizontal plane.

The hollow member 20 is provided therein with laser beam paths 20a, 20bwhich intersect at right angles. In the laser beam path 20a, there isprovided a laser diode (i.e. semiconductor laser, light source) 23 whichemits a visible laser, a collimating lens 24 and a laser beamcross-sectional shape converting optical system 18 which is comprised ofa pair of anamorphic prism 25, 26 (refer to FIG. 4). The laser beam path20b, which extends in the direction of the rotational axis "a" isprovided therein with a projecting optical system 22.

The projecting optical system 22 (FIG. 2) is provided with a PBS 27(i.e. polarizing beam splitter) which receives a laser beam emitted fromthe anamorphic prism 26 (FIG. 4). The PBS 27 has a polarizatingseparating plane 27a. A quarter-wave plate (1/4 λ plate) 28 is adheredto the upper surface of the PBS 27 such that the optical axis of thequarter-wave plate 28 is inclined at 45 degrees with respect to thepolarization direction of the incident light. The quarter-wave plate 28is coated at the upper surface thereof with a optical thin film 28awhose reflectance is approximately 10% to 20%, to allow the majority ofthe incident beam to pass therethrough toward a pentagonal prism 35. Theresidual laser beam is reflected to the polarization separating plane27a of the PBS 27. The quarter-wave plate 28 converts the linearlypolarized laser beam, which has been reflected by the polarizationseparating plane 27a in the PBS 27, into a circularly-polarized laserbeam. Most of this circularly-polarized laser beam is mostly transmittedto the pentagonal prism 35 through the optical thin 28a. The remainingpart of the circularly polarized laser beam, which does not pass throughthe optical film 28a, is reflected by the same back downwards againpassing through the quarter-wave plate 28 to be converted into alinearly-polarized laser beam having a perpendicular polarizationdirection, i.e. it is rotated by 90 degrees, compared with the directionprior to being incident on the quarter-wave plate 28. Therefore, thelaser beam which has been reflected by the optical thin film 28a, passesthrough the quarter-wave plate 28 to be incident upon the polarizationseparating plane 27a, it then passes through the polarization separatingplane 27a without being reflected by the polarization separating plane27a, that is, without returning to the laser diode 23.

Wedge prisms 29a, 29b are provided at a lower portion of thepolarizating beam splitter 27 as shown in FIG. 1 and FIG. 2.

A front lens group 31 and a rear lens group 32 are provided andconstitute a Galilleo-type beam expander B, above the PBS 27 in FIG. 1and FIG. 2. The beam expander B is used for adjusting the beam diameterof a parallel laser beam which has been collimated by the collimatinglens 24 and whose cross-sectional shape has been changed into a circularshape by the laser beam cross-sectional shape converting optical system18. The beam expander B also constitutes a beam waist position changingoptical system of the present invention, and the details thereof will bedescribed later.

The rear lens group 32 is fixed to the hollow member 20 in the laserbeam path 20b. The front lens group 31 is fixed to a sliding cylindricalmember 30, which is slidable within the optical path 20b in the opticalaxis direction (vertical direction), i.e. the front lens group 31 ismovable along the rotational axis "a" with respect to the hollow member20.

The rotatable laser emitter 15 is provided therein with a laser beampath 15a whose lower end is aligned to the upper end of the laser beampath 20b, and a pentagonal prism accommodating section 15b, formed atthe top of the rotatable laser emitter 15, having a diameter larger thanthat of the laser beam path 15a. A projection opening or window 33 isformed on a side wall of the pentagonal prism accommodating section 15b.The laser beam incident on and deflected by the pentagonal prism 35 isprojected, in a direction towards the outside of the rotatable laseremitter 15 through the projection window 33. The pentagonal prismaccommodating section 15b has an open upper end. The optical axis "a" isaligned with the center axis of a transmitting member 36 which is fittedin the upper central part of the circular hole 16a of the transparentmember 16.

The pentagonal prism 35 is fixed to the rotatable laser emitter 15 ofthe projector 13 so as to rotate together and constitutes a reflectingmeans for reflecting a laser beam on the rotational axis "a." As shownin FIG. 2, the pentagonal prism 35 includes an incident surface 35c uponwhich the laser beam exited from the rear lens group 32 is incident; afirst reflecting surface 35a which is inclined at a predetermined anglewith respect to the incident surface 35c and which is provided with aoptical thin film 14 whose reflectance is around 70-80%, so that thoselaser beams incident upon the incident surface 35c are made incidentupon the first reflecting surface 35a; a second reflecting surface 35bwhich is angled relative to the first reflecting surface 35a by an angleθ of 45 degrees, and reflects the laser beam reflected by the firstreflecting surface 35a; and a exit surface 35d which is perpendicular tothe incident surface 35c and from which the laser beam reflected by thesecond reflecting surface 35b is projected outwards. A reflecting filmis formed on the second reflecting surface 35b through aluminum vapordeposition or the like. Also, a wedge-type prism 34 is fixed on thefirst reflecting surface 35a with the optical thin film 14 sandwichedtherebetween. This wedge-type prism 34 is designed such that when theoblique surface thereof is attached to the first reflecting surface 35a,the upper exit surface 34a of the wedge-shaped prism 34 is parallel withthe incident surface 35c of the pentagonal prism 35.

The hollow member 20 is provided integral with a driving arm 37, whichextends rightwardly in FIG. 1, and a driving arm 39 (FIG. 3) whichintersects at right angles with the driving arm 37, within a planeperpendicular to the surface of FIG. 1. These driving arms 37, 39 arebent and downwardly inclined at the upper part of the bulged section 21and are respectively provided on the front ends thereof with rollers 40,41 mounted so that their centers are located in the same plane as thecenter of the spherical part of the bulged section 21.

The housing 12 is provided on the inner wall thereof with a bracket 42which projects inwardly in a horizontal direction. A gear supportinghole 42a is formed on this bracket 42. The housing 12 is provided on theupper wall 12b with a gear supporting hole 43 which is aligned with thegear supporting hole 42a, so that the shaft of an adjusting screw 45 isrotatably fitted at the opposite ends thereof in the gear supportingholes 42a and 43. The bracket 42 holds a first level adjusting motor 44secured thereto. The rotary shaft of the first level adjusting motor 44has a pinion 49 secured thereto, which is engaged with a transmissiongear 50 secured to the lower end portion of the adjusting screw 45. Anadjusting nut 46 is screw-engaged with the adjusting screw 45, so thatthe adjusting nut 46 and the adjusting screw 45 constitute a feed screwmechanism. The adjusting nut 46 is provided on the outer peripheralsurface thereof, with an outwardly projecting operation pin 47 whichabuts against the roller 40 from above. The rotation of the adjustingnut 46 relative to the housing 12 is restricted by a supporting memberor mechanism (not shown).

As shown in FIG. 3, the housing 12 is provided on the inner wall thereofwith an inwardly projecting bracket 78 which is in turn provided with agear supporting hole (not shown) which is aligned with a similar gearsupporting hole (not shown) formed on the upper wall 12b of the housing12 (similar in manner to the holes 42a and 43 mentioned above).Non-threaded lower and upper portions formed on both ends of anadjusting screw 79 are rotatably engaged with the gear supporting holes42a, 43, respectively. A second level adjusting motor 75 is fixed on thebracket 78.

The drive shaft of the second level adjusting motor 75 has a pinion 76secured thereto, which is in mesh with a transmission gear 77 fixed tothe lower end portion of the adjusting screw 79. An adjusting nut 80 isscrew-engaged with the adjusting screw 79, so that the adjusting nut 80and the adjusting screw 79 constitute a feed screw mechanism. Theadjusting nut 80 is provided on the outer peripheral surface thereof,with an outwardly extending operation pin 81 which abuts against theroller 41 from above. The rotation of the adjusting nut 80 relative tothe housing 12 is restricted by a supporting member or mechanism (notshown).

The housing 12 is provided on the inner wall thereof with a supportingprojection 51 which is located by bisecting the angle defined betweenthe arms 37 and 39. A stretched coil spring 52 is provided between thesupporting projection 51 and the hollow member 20. The hollow member 20is biased by the coil spring 52 such that the upper side of the rollers40, 41 press against the lower side of the contact pins 47, 81 with acommon biasing force, respectively. Namely, the hollow member 20 isbiasing at the lower end thereof toward the supporting projection 51,while the bulged portion 21 is supported by the circular hole 19a, sothat the angular position of the hollow member 20 in the horizontaldirection can be adjusted through the contact pins 47, 81, which aremoved up and down by an actuation of the first-level and second-levelmotors 44, 75, respectively, which are actuated in accordance withsignals outputted from a microcomputer 82.

The hollow member 20 is provided at a lower portion thereof withbrackets 70, 71 extending perpendicular to each other in a horizontalplane (FIG. 3), in a direction opposite to the direction of the drivingarms 37 and 39, respectively. Level detecting sensors 72, 73 are mountedto both brackets 70, 71, respectively. Detecting signals outputted fromthe level detecting sensors 72, 73 are sent to the microcomputer 82. Atemperature detecting means 90, such as a thermistor which detects airtemperature in the laser surveying device 11, is electrically connectedto the microcomputer 82.

The hollow member 20 is formed at the lower portion thereof with abracket 53 which extends horizontally. A bracket 55 extends horizontallyfrom the hollow member 20, and is positioned above and opposed to thebracket 53. The brackets 53 and 55 are respectively formed with opposedgear supporting holes 53a, 55a, so that the shaft of a lens moving screw56 is rotatably fitted at the opposite ends thereof in the correspondinggear supporting holes 53a, 55a. A beam diameter adjusting motor 59 isfixed on the bracket 53. A pinion 60 fixed on a rotary shaft of the beamdiameter adjusting motor 59 is engaged with a transmission gear 61 fixedto the lower end portion of the adjusting screw 56. An adjusting nut 57is engaged with the adjusting screw 56. The adjusting nut 57 and theadjusting screw 56 constitute a feed screw mechanism.

An insertion opening 63 is formed on the hollow member 20 in a positionto correspond to the sliding cylindrical member 30 placed in the hollowmember 20. The adjusting nut 57 and the sliding cylindrical member 30are connected to each other by a linking member 62 having an invertedL-shaped cross section. The upper end of the linking member 62 isinserted into the insertion opening 63 and is fixed to the lower end ofthe sliding cylindrical member 30, while the lower end of the linkingmember 62 is fixed to the outer upper peripheral surface of theadjusting nut 57.

With the above arrangement, actuation of the beam diameter adjustingmotor 59, in accordance with signals outputted from the microcomputer82, causes the beam diameter adjusting nut 57 to vertically move throughthe pinion 60, the transmission gear 61 and the lens moving screw 56,and thereby the front lens group 31 is moved relative to the rear lensgroup 32 through the linking member 62 and the sliding cylindricalmember 30, and thereby a beam diameter of a collimated laser beam L₁ canbe adjusted so as to change the beam waist position of the laser beam L₃projected from the rotatable laser projector 15.

A bracket 65 is provided on the uppermost part of the hollow member 20,onto which a motor 66 is fixed. A pinion 67 fixed on a rotary shaft ofthe motor 66 is engaged with a transmission gear 69 which is fixed to anouter peripheral surface of the rotatable laser emitter 15. With thisstructure, the actuation of the motor 66, in accordance with signalsoutputted from the microcomputer 82, causes the rotatable laser emitter15 to rotate in relation to the hollow member 20, through the pinion 67and the transmission gear 69.

A rotation detecting sensor 83, having an upwardly extending end, isprovided on the top of the hollow member 20, on the opposite side of thebracket 65 with respect to the axis "a." The rotation detecting sensor83 is provided with a light emitter and a light receiver (both notshown). The light emitter emits light upwardly towards the transmissiongear 69 and subsequently the light receiver receives the light reflectedby a reflection plate (not shown) that has a predetermined pattern andis provided on the lower surface of the transmission gear 69, so as toconvert the detected light into electric signals which it then sends tothe microcomputer 82. The microcomputer 82 calculates a rotation anglefor the rotatable laser emitter 15 in accordance with the inputtedsignals.

The laser beam cross-sectional shape conversion optical system 18, asshown in FIG. 4, is provided with anamorphic prisms 25, 26 which arelinearly arranged on the optical axis of a laser beam emitted by thelaser diode 23. Apex angles of the anamorphic prism 25, 26 are α1, α2,respectively, and the prisms 25 and 26 are arranged such that thedirections in which a laser beam is refracted are opposite to eachother. The prisms 25 and 26 work in such a way so as to make a laserbeam incident on prism 25 and a laser beam emitted from the rear surfaceof prism 26, parallel to each other. The collimating lens 24, locatedbetween the anamorphic prism 25 and the laser diode 23, is arranged soas to have a sufficiently large numerical aperture and provides apredetermined incident angle "i" of light incident upon the anamorphicprism 25.

A laser beam emitted from the laser diode 23, having an elliptic-shapedlight intensity distribution on a cross section perpendicular to thedirection of the laser beam, is converted, through the collimating lens24, into a collimated beam which has an elliptic-shaped cross sectionperpendicular to the direction of the laser beam. The aboveelliptic-shaped cross section includes a minor axis Da and a major axisDb, perpendicular to each other as shown in FIG. 5. When the above laserbeam passes through the laser beam cross-sectional shape conversionoptical system 18, its elliptic-shaped cross section is converted into asubstantially circular-shaped cross section (FIG. 6) in a manner suchthat the minor axis Da is extended to Da' whose length is substantiallyequal to that of the major axis Db' corresponding to the major axis Db.

The control of the beam expander B which adjusts the beam waist positionin accordance with a variation in temperature, will be hereinafterdescribed.

In FIG. 7, the beam expander B is comprised of a front lens group 31having a focal length f₁ (f₁ <0) and a rear lens group 32 having a focallength f₂ (f₂ >0). The two lens groups are used for making a laser beam,which when incident on the front lens group 31 has a diameter D_(i),into a laser beam having a diameter D_(o) when projected from the rearlens group 32. The initial distance between the front and rear lensgroups 31, 32 is designated by "d" in FIG. 7. The beam expander B isconstituted such that a deviated or shifted beam waist position, causedby a variation in temperature or the like, can be adjusted for byvarying the initially set distance "d" between the front and rear lensgroups 31, 32. The amount the front lens group 31 shifts relative to therear lens group 32 is designated by "δ" as shown in FIG. 7.

The initial distance "d" is formulated by the following equation.

    d=(f.sub.1 +f.sub.2 +ΔL

In the case where a laser beam projected from the laser surveying device11 is a Gaussian beam, the beam waist is formed at a position E awayfrom the rear lens group 32 by a distance Xs, and the diameter of thisbeam waist is Wx. The above relationships are defined by the followingequations:

    Wx=m×Di/{1+(m.sup.4 ×α.sup.2 /f.sub.2.sup.4)×ΔL.sup.2 }.sup.1/2            (1)

    Xs=f.sub.2 +[(m×α).sup.2 /{(f.sub.2 /m).sup.2 +(m×α/f.sub.2).sup.2 ×ΔL.sup.2 }]×ΔL(2)

wherein α is equal to "π×Di² /4λ,"

λ represents the wave length of incident light, and

m is equal to "|f₂ /f₁ |."

In this case, a radius of curvature R (shown in FIG. 7) of thewavefront, at the laser beam projecting opening in the rear lens group32, is defined by the following equation (3):

    R=Xs×{1+(π×Wx.sup.2 /4λ×Xs).sup.2 }(3)

In the case when one of the lens groups (the front lens group 31 in FIG.7) is shifted from the initially set distance d by the amount δ, thebeam waist position shifts to a position F away from the rear lens group32 by a distance Xs', and the beam waist diameter becomes Wx'. Thedistance Xs' and the beam waist diameter Wx' can be obtained by theabove equations (1) and (2) by simply replacing "ΔL" therein with"ΔL+δ". In this case, the radius of curvature R' of the wavefront at thelaser beam projecting opening, which changes due to the shifting of thefront lens group 31, can be obtained by equation (3) by simply replacing"Xs" and "Wx" with "Xs'" and "Wx'", respectively.

In other words, the movement of one of the lens groups in the beamexpander B causes the radius of curvature of the wavefront, at the laserbeam projecting opening, to change from "R" to "R'", thereby the beamwaist position and the diameter of the beam waist can be changed oradjusted from "Xs" to "Xs'" and from "Wx" to "Wx'", respectively.

Variations in the position and diameter of the beam waist caused by avariation in temperature of Δt will be explained with reference to FIG.8.

In the laser surveying device 11, the laser beam emitted from the laserdiode 23 is collimated by the collimating lens 24, having a focal lengthfc, so as to change the incident laser beam into a collimated laser beamhaving the diameter Di. This collimated laser beam is subsequently madeincident on the front lens group 31, which has a focal length f₁.Thereafter, the diameter Di is enlarged and exited from the rear lensgroup 32 (focal length is f₂) as a beam having the diameter Do. As haspreviously been described above, when the distance between the frontlens group 31 and the rear lens group 32, of the distance from the rearlens group to the beam expander B, is initially set as the distance "d",the distance from the rear lens group 32 to the beam waist position is"Xs", the beam waist diameter is "Wx" and the radius of curvature of thewavefront of the laser beam, projected from the rear lens group 32, is"R".

When temperature changes occur under the above condition, the beam waistposition shifts due to either an extension or a contraction of a lenssupporting frame, which supports the front lens group 31, the rear lensgroup 32 or the collimating lens 24; and/or a variation in therefractive index of the front lens group 31, the rear lens group 32 orthe collimating lens 24, etc. This is particularly so when a temperaturevariation causes an extension or contraction of the lens supportingframe 230, which will cause a change in the distance P, namely thedistance between the laser diode 23 and the collimating lens 24. Theeffect of this is the main cause of the shift in the beam waistposition. The reason for this is that when the distance P changes, dueto a variation in temperature, the radius of curvature of the wavefrontof the laser beam emitted from the collimating lens 24 changes, therebythe radius of curvature R of the wavefront of the laser beam emittedfrom the rear group lens 32 changes, and thus the beam waist distance Xsand the diameter of the beam waist Wx consequently change. Some examplesillustrating these changes have already been discussed with reference toFIGS. 66 and 67.

If one of the lens groups (the front lens group 31 in FIG. 8) of thebeam expander B is adjusted to move along the optical axis by a certainamount, so as to offset a shift of the beam waist position due to avariation in temperature, the laser surveying device 11 is able toproject a laser beam without any variance in either the beam waistdistance Xs or the beam waist diameter Wx. Therefore, if data, relatingto variations of the beam waist position caused by variations intemperature and variations of the beam waist position correspond tovariations of the beam waist position caused by a shift of one of thelens groups of the beam expander B, is previously prepared (i.e. storedin the memory of a microcomputer), influences upon the beam waistposition and the beam waist diameter can be easily eliminated inaccordance with the above data.

Several examples, constructed to realize the above-mentioned matter,will be hereinafter explained with reference to FIG. 8. In the firstexample, the focal length fc, of the collimating lens 24, is 6 mm; thelaser beam diameter Di, projected from the collimating lens 24, is 6 mm;the focal length f₁, of the front lens group 31, is -78.7 mm; the focallength f₂, of the rear lens group 32, is 104.9 mm; the magnification "m"(|f₂ /f₁ |) is 1.33; the projected laser beam diameter Do, from the rearlens group 32, is 8 mm; the initially-set distance d, between the frontlens group 31 and the rear lens group 32, is 26.34 mm; ΔL isapproximately 0.14 mm; the radius of curvature R, of the wavefront ofthe laser beam emitted from the rear lens group 32, is 78 m; the beamwaist distance Xs is 39.578 m; and, the beam waist diameter Wx is 5.7mm.

In the second example of the first embodiment, the focal length f₁, ofthe front lens group 31, is -43.2 mm; the focal length f₂, of the rearlens group 32, is 90.8 mm; the magnification "m" (|f₂ /f₁ |) is 2.08;the projected laser beam diameter Do, from the rear lens group 32, is12.5 mm; the initially set distance d, between the front lens group 31and the rear lens group 32, is 47.64 mm; ΔL is approximately 0.04 mm;the radius of curvature R of the wavefront of the laser beam, emittedfrom the rear lens group 32, is 190 m; the beam waist distance Xs is96.605 m; and, the beam waist diameter Wx is 8.8 mm. The focal length fcand the laser beam diameter Di are the same as those in the above firstexample.

As described above, FIG. 14 shows the variation of the beam diameter atdifferent distances from the laser surveying device 11, having thedesign of the above first example, when the initial inside temperature(initially set at 20° C.) in the device 11 changes to 50° C. and to -20°C., under the condition that the initial beam waist position Xs isapproximately 39.578 m. As shown in FIG. 14, the beam waist positions at50° C. and -20° C. are 29.646 m and -38.203 m ("-" indicates a directionopposite to the laser beam advancing direction), respectively.

Likewise, FIG. 13 shows the variation of the beam diameter at differentdistances from the laser surveying device 11, having the design of theabove second examples when the initial inside temperature (initially setat 20° C.) in the device 11 changes to 50° C. and to -20° C., under thecondition that the beam waist position Xs is approximately 96.605 m whenthe initial inside temperature in the device 11 is 20° C. As shown inFIG. 13, the beam waist positions at 50° C. and -20° C. are 63.944 m and-94.255 m, respectively.

FIGS. 9 and 10 show variations in the beam diameter at each projectiondistance when the shifting amount δ is changed from its initial amountof zero (0.00 mm), wherein the initial amount of zero is initially setat a predetermined distance between the front lens group 31 and the rearlens group 32. In FIGS. 9 and 10, the horizontal axis shows the beamprojection distance from the laser surveying device 11, and the verticalaxis shows the beam diameter at the corresponding beam projectiondistance.

In FIG. 9, a beam expander B of the first example, having a beammagnifying power of 1.33 is used, and the amount of shifting δ isbetween -0.05 mm and +0.05 mm ("+" herein indicates a shift by the frontlens group 31 away from the rear lens group 32). As can be seen in FIG.9, the beam waist diameters at respective amounts of shifting δ (i.e.δ=0 mm, -0.05 mm, and +0.05 mm) concentrate within a range from 25 m to50 m. When the amount of shifting δ is changed from 0 mm to +0.05 mm,the beam waist position shifts towards the rear lens group 32 and thebeam waist diameter at a long distance (i.e. 200 m) exceeds the beamwaist diameter when no shifting occurs (i.e. 0 mm), i.e. the beam waistdiameter shown on curve (f) in FIG. 9.

On the other hand, when the amount of shifting δ is changed from 0 mm to-0.05 mm, the beam waist position shifts towards the rear lens group 32by an amount larger than the above case, where the shifting amount δ ischanged from 0 mm to +0.05 mm, and the beam waist diameter at a longdistance falls below the beam waist diameter of the case where theamount of shifting δ is zero (0 mm), as shown in FIG. 9.

In FIG. 10, the beam expander B of the second example, having a beammagnifying power of 2.08, is used and the amount of shifting δ isbetween -0.05 mm and +0.05 mm, as above. When the amount of shifting δis changed from 0 mm to +0.05 mm, the beam waist position shifts towardsthe rear lens group, and the beam waist diameter at a long distanceexceeds the beam waist diameter of the case where the amount of shiftingδ is zero (0 mm), i.e. the beam waist diameter on a curve (i) shown inFIG. 10.

On the other hand, when the amount of shifting δ is changed from 0 mm to-0.05 mm, the beam waist position shifts towards the rear lens group 32by an amount larger than the above case (where the shifting amount δ ischanged from 0 mm to +0.05 mm), and the beam waist diameter at a longdistance exceeds, in substantially the entire distance range, the beamwaist diameter of the case where amount of shifting δ is zero (0 mm), asshown in FIG. 10.

Accordingly, if the front lens group 31 is adjusted to move along theoptical axis toward or away from the rear lens group 32, so as to changethe shifting amount value δ from 0.00 mm to -0.05 mm or to +0.05 mm, the(beam diameter) curves (f), (i) can be varied to the curves (g), (j),respectively, while the (beam diameter) curves (g), (j) can be varied tothe curves (h), (k), respectively.

Given the above information, numerical values of respective beam waistpositions obtained when the amount of shifting δ is variously changed,are previously stored as data in a microcomputer 82. Then if the frontlens group 31 is adjusted to move along the optical axis, in accordancewith the stored data, so as to compensate variations in the beam waistposition caused by variations in temperature, the beam waist positioncan be maintained at any desired position, regardless of temperature.

A method of driving the front lens group 31 by the microcomputer 82,which inputs a temperature detection signal outputted through atemperature detection means 90, and also a method of controlling thebeam waist position will be hereinafter described.

A storing portion (not shown) of the microcomputer 82 stores the datacontaining the relationship between the temperature, detected by thetemperature detecting means 90, and the shifting amount δ of the frontlens group 31, used for correcting the beam waist position changed by avariation in temperature. The data contains, for each beam expander B(one having a beam magnification of 1.33 and the other of 2.08), therelationship between the shifting amount δ that is necessary to maintainthe beam waist position in, substantially, a fixed position inaccordance with the detected temperature, and respective detectedtemperatures, on the basis that the shifting amount δ of the front lensgroup 31 is zero when the beam waist position is at its preset initialposition at a standard temperature of 20° C. Table 1-0 below shows theabove relationship for each beam expander B.

                  TABLE 1-0                                                       ______________________________________                                                    +50° C.                                                                        +20° C.                                                                        0° C.                                                                           -20° C.                           ______________________________________                                        Mag. 1.33 δ (mm)                                                                          -0.020    0.000 0.023  0.046                                Mag. 2.08 δ (mm)                                                                          -0.022    0.000 0.016  0.035                                ______________________________________                                    

Accordingly, when the microcomputer 82 outputs a drive signal to thebeam diameter adjusting motor 59, in accordance with the temperaturesignal detected by the temperature detecting means, so as to move thefront lens group 31 relative to the rear lens group 32 by the shiftingamount δ corresponding to the detected temperature, the beam diameteradjusting motor 59 rotates and the beam waist position, deviated fromits initial position due to a variation in temperature, is adjusted tomove back to its initial position. According to the laser surveyingdevice 11 to which the present invention is applied, the beam waistposition of each of the projected laser beams L₃ and L₄, that isdeviated or shifted due to a variation in temperature, is controlled bythe microcomputer 82 in the above-noted manner, thereby the lasersurveying device 11 can be provided in which the variation of the beamwaist position is minimized.

The surveying operation of the laser surveying device 11 will behereinafter explained.

Firstly, the laser surveying device 11 is placed, at a predeterminedposition, on a tripod. Secondly, the rotational axis "a" of therotatable laser emitter 15 is adjusted so as to extend in the verticaldirection, since the rotational axis "a" is usually somewhat inclinedrelative to the vertical direction immediately after the device 11 hasbeen placed at a predetermined position on the tripod. At this time, thelevel detection sensors 72, 73 detect a non-horizontal position, i.e. astate where the rotational axis "a" does not extends in the verticaldirection. In this state, turning a drive switch on (not shown), themicrocomputer 82 calculates an angle of deviation value in accordancewith signals received from the level detection sensors 72, 73 and thenactuates the first and second level control motors 44 and 45 inaccordance with the calculated angle of deviation value.

For example, when the first level adjusting motor 44 is actuated, therotation of the motor 44 is transmitted to the adjusting screw 45through the pinion 49 and the transmission gear 50. Rotation of theadjusting screw 45 moves the adjusting nut 46 upwardly and downwardly.When the roller 40, biased by the stretched coil spring 52 in thepredetermined direction, comes into contact against the pin 47 of theadjusting nut 46, the rotatable laser projector 15 can be adjusted so asto be inclined relative to the vertical direction by means of rotatingor inclining the hollow member 20 around the center of the bulgedportion 21.

On the other hand as can be seen in FIG. 3, when the second leveladjusting motor 75 is actuated, the rotation of the motor 75 istransmitted to the adjusting screw 79 through the pinion 76 and thetransmission gear 77. Rotation of the adjusting screw 79 moves theadjusting nut 80 upwardly or downwardly. When the roller 41, biased bythe stretched coil spring 52 in the predetermined direction, comes intocontact against the pin 81 of the adjusting nut 80, the rotatable laserprojector 15 can be adjusted so as to be inclined relative to thevertical direction by means of rotating or inclining the hollow member20 around the center of the bulged portion 21.

The above adjusting operation of the projector 13 continues untildetection values of the level detection sensors 72, 73 come to be closeto the standard value of a horizontal position and the angle deviationvalue calculated by the microcomputer 82 finally becomes zero. By theabove-noted adjusting operation, the projector 13 including therotatable laser projector 15, is precisely adjusted to be at ahorizontal position so that a laser beam is horizontally projected fromthe laser surveying device 11. The leveling operation is accordinglycompleted.

The laser surveying device 11, with the above-noted structure, isoperated as follows. Turning a main switch ON (not shown), the laserdiode 23 is actuated in accordance with a signal received from themicrocomputer 82 to emit a laser beam. This emitted laser beam isconverted by the collimating lens 24 into a collimated laser beam havingan oval-shaped cross section, and the collimated laser beam is thenincident upon the anamorphic prism 25 of the optical system 18. Theanamorphic prisms 25, 26 enlarge the laser beam along the minor axis Da(see FIG. 5) so as to convert the cross section of the laser beam froman oval-shaped into a circular-shaped cross section with the diameterDa' as shown in FIG. 6. This laser beam having a circular-shaped crosssection is divided by the PBS 27 into an upwardly-advancing laser beamL₁ and a downwardly-advancing laser beam L₂ (see FIG. 2).

In FIG. 2, when the laser beam L₀, incident on the PBS 27, is a laserbeam having an polarization direction perpendicular to the incidentplane, which includes the laser beam L₀ and a normal "n", of thepolarization separating plane 27a, the laser beam L₀ is entirelyreflected on the polarization separating plane 27a and deflected by 90degrees to advance upwardly. Because the quarter wave plate 28 isattached to the PBS 27 in a manner such that the optical axis of thequarter-wave plate 28 is oriented at 45 degrees relative to thedirection of polalization of the laser beam incident on the quarter-waveplate 28, the laser beam L₀ is changed into a circularly-polarized laserbeam L₁ to advance towards the pentagonal prism 35, after passingthrough the quarter-wave plate 28. Part of the laser beam L₁ isreflected by the semi-transparent film 28a back towards the polarizationseparating plane 27a and again passes through the quarter-wave plate 28and is thereby converted into a linearly-polarized light having adirection of polarization. perpendicular to that of the previouslinearly-polarized light. That is, the linearly-polarized laser beamwhich is incident upon the polarization separating plane 27a with anS-polarization and reflected upwards, consequently moves toward thepolarization separating plane 27a with a P-polarization relative to thepolarization separating plane 27a. Thereafter, this downwardly-advancinglinearly-polarized laser beam of P-polarization passes thorough thepolarization separating plane 27a totally, and subsequently, passesthrough wedge prisms 29a, 29b and advances downwardly out of the lasersurveying device 11 as laser beam L₂.

On the other hand, the upwardly-advancing laser beam L₁ passes throughthe front and rear lens groups 31 and 32, then passes through theincident surface 35c of the pentagonal prism 35, to be deflected atright angles by the first and second reflection surfaces 35a and 35b soas to be projected, from the projecting surface 35d, in a horizontaldirection as the laser beam L₃. Part of the laser beam L₁, not reflectedby the first reflection face 35a, passes through a half mirror plane,formed by the contacting part between the first reflecting plane 35a ofthe pentagonal prism 35 and the wedge-type prism 34, to be projectedupwards from the projecting surface of the wedge-type prism 34 as thelaser beam L₄.

Accordingly, the laser beam L₀ emitted from the laser diode 23 isfirstly divided into the laser beams L₁ and L₂, which proceed verticallyin opposite directions. Subsequently, the laser beam L₁ is divided intothe upwardly-advancing laser beam L₄ and the horizontally-advancinglaser beam L₃, perpendicular to the laser beam L₄.

When the motor 66 of the laser surveying device 11 is driven at apredetermined R.P.M. in response to the main switch being turned ON, therotation of the motor 66 is transmitted to the rotatable laser projector15, through the pinion 67 and the transmission gear 69, thereby rotatingthe rotatable laser projector 15, relative to the bulged portion 21.Therefore, the laser surveying device 11 deflects the laser beam L₁,projected from the rear lens group 32, by 90° through the pentagonalprism 35. The laser beam L₃ will continue to be projected horizontallywhile the rotatable laser projector 15 is rotated about the rotationalaxis "a". This laser beam L₃ is continuously projected at a fixed levelof intensity from the rotating rotatable laser projector 15, to form ahorizontal reference plane.

At this time, even if the beam waist position of the laser beam L₃ isdeviated from its initial position due to a variation in temperature inthe laser surveying device 11, the microcomputer 82 controls the frontlens group 31 to move relative to the rear lens group 32, in accordancewith a temperature signal received from the temperature detection means90, by the shifting amount δ corresponding to the detected temperatureto thereby maintain the beam waist position at its initial position.

In the case of focalizing the laser beam, projecting from the lasersurveying device 11, on an object such as a wall, a pillar, etc., aswitch (not shown) is manually operated to actuate the beam diametercontrol motor 59 in a forward or reverse direction. The rotation of thebeam diameter control motor 59 is transmitted to the beam diameteradjusting screw 56 through the pinion 60 and the transmission gear 61.The rotation of the beam diameter adjusting screw 56 moves the beamdiameter adjusting nut 57 in an upwards or downwards direction, so thatthe upward Or downward movement of the nut 57 is transmitted to thesliding cylindrical member 30 through the link 62. The focal point ofthe projecting laser beam on an object such as a wall, a pillar, etc.,is adjusted by manually operating the above-noted motor operatingswitch, while observing the beam spot of the projecting laser beamprojected on the object.

Since the laser surveying device 11 also has the ability to emit thelaser beam L₂ vertically downwards towards the ground, the rotationalaxis "a" of the projector 13 can be moved to a location above apredetermined point on the ground, simply by manually moving the lasersurveying device 11 and aligning the beam spot of the laser beam L₂ withthe above predetermined point.

Other embodiments of the present invention will be described below withreference to FIGS. 11 and 12. These figures show the relationshipbetween the shifting amount δ of the front lens group 31 and thetemperature T, detected by the temperature detecting means 90. Thisrelationship is used to adjust a deviation of the beam waist positionwhen the microcomputer 82 operates to adjust the beam waist positionwhen the temperature in the device 11 varies from a standard temperature(+20° C.). In FIGS. 11 and 12 the magnifying power of the beam expanderB is 1.33 and 2.08, respectively. In these figures, the shifting amountδ and the temperature T have a substantially linear relationship, thus,the relation therebetween can be defined approximately by a primaryfunction. That is, the relation can be defined by the following equation(4):

    δ=aT+b                                               (4)

Consequently, if the value of inclination "a" and intercept "b" in theabove equation are initially stored in a storing portion of themicrocomputer 82, the shifting amount δ of the front lens group 31 canbe detected in accordance with such data stored in the above storingportion and the detected temperature.

With the above arrangement, even if the beam waist position of the laserbeam L₃ deviates from its initial position due to a variation intemperature in the actual laser surveying device 11, the microcomputer82 calculates the shifting amount δ corresponding to the detectedtemperature and controls the front lens group 31 to move relative to therear lens group 32, in accordance with a temperature signal receivedfrom the temperature detection means 90, by the calculated shiftingamount δ to thereby maintain the beam waist position at its initialposition.

As can be seen from the foregoing, according to the present invention, astable and highly precise beam projection device can be provided, whichallows only a minimum variation in the beam diameter, by means ofcontrolling the beam waist position of the projecting laser beam after avariation in temperature.

An embodiment has been described in which the beam waist position isautomatically controlled by a microcomputer, so as to keep a constantbeam waist position, in accordance with temperature change, based onpreviously memorized temperature data. Another embodiment to which asecond aspect of the present invention is applied will now be described,in which a beam waist position is prevented from changing due totemperature characteristics of the lens holding frame and lensesthemselves. This description will be accompanied with reference to FIGS.15 to 58. Note that the laser surveying device of this embodiment isidentical in appearance with that of FIGS. 1 to 4, so detailedexplanation will be omitted.

According to this embodiment, the collimating lens 24 and the hollowmember 20 are formed so as to mutually offset: (a) a change in distancebetween the point where the laser is initially emitted and thecollimating lens 24, generated by contractions and expansions of thehollow member 20, due to variations in temperature, and (b) focal pointmovements due to changes in the refractive index and/or radius ofcurvature of the collimating lens 24, caused by the glass material ofwhich the collimating lens 24 is made. That is, the specific expansionfactor and the refractive index variation factor of each material usedto form the collimating lens 24 and the hollow member 20, and also thesize and shape thereof, are determined so as to prevent the diverging orconverging state of the laser beam, emitted from the collimating lens24, from varying. Further, the material used and the shape of thecollimating lens 24 are determined so as to correct axial chromaticaberration and to prevent the diverging or converging state of the laserbeam, emitted from the collimating lens 24, from varying even if theoscillation wavelength of the laser beam emitted from the semiconductorlaser 23 changes due to a variation in temperature.

The power distribution and Abbe numbers of the beam expander B,comprising a front lens group 31 having a negative power and a rear lensgroup 32 having a positive power, are determined so as to prevent thediverging or converging state of the laser beam, emitted from the beamexpander B, from varying due to changes in wavelength.

It is noted that the laser surveying device 11 according to the firstembodiment to which the second aspect of the present invention isapplied (explained herein below), is constructed such that the divergingor converging state of the emitted laser beam is hardly subject tovariations in temperature, inside, substantially, the whole of theoptical system in the laser surveying device 11 for projecting the laserbeam from the rotatable beam emitter 15, since the collimating lens 24is provided with a function that compensates for the effects oftemperature and also with a chromatic aberration correcting function,and further the beam expander B is provided with a chromatic aberrationcorrecting function.

Because the collimating lens 24 is arranged to have a positive power, itis necessary for the collimating lens 24 to be comprised of at least onepositive lens, and at least one negative lens, for correcting sphericalaberration. In particular, when it is desired to obtain a particularlyfast collimating lens, it is preferable that the positive lens in thecollimating lens be comprised of more than one lens. In this embodiment,the collimating lens 24 has a numerical aperture of 0.50, and iscomprised of three positive lenses and one negative lens. The threepositive lenses are used for effectively collecting the laser beamemitted by the semiconductor laser 23, while the single negative lens isused for shortening the whole length of the collimating lens 24.

As a result of temperature variations, the variation of the laser beamemitted from the collimating lens 24 can be considered to be caused byan out-of-focus condition which results from the following twovariations--firstly, the variation of the distance between the laserdiode 23 and the collimating lens 24, and secondly, the variation of thefocal point of the collimating lens 24. For example, supposing that thecollimating lens 24 is formed as an extremely thin lens, having next tono thickness, having a focal length f, made of a material having alinear expansion coefficient α₁, a refractive index n, a temperaturecoefficient β₁ of refractive index, and, is supported by a lenssupporting member which has a linear coefficient index α₂ and has a setpredetermined distance between the laser diode 23 and the collimatinglens 24, the deviation amount, ΔX₁, of the focal point of thecollimating lens 24 is defined by the following equation, due to theeffect of an extended focal length by a linear expansion of thecollimating lens 24 and also the effect of the variation of refractiveindex in the collimating lens 24 when the temperature varies by anamount ΔT.

    ΔX.sub.1 =f{α.sub.1 -β.sub.1 /(n-1)}×ΔT

When it is assumed that the collimating lens 24 is formed as anextremely thin lens, with next to no thickness, as noted above, thedeviation amount ΔX₂, of the distance between the laser diode 23 and thecollimating lens 24, is obtained by the following equation since thefocal length of the collimating lens 24 becomes equal to the distancebetween the laser diode 23 and the collimating lens 24 according to theabove assumption.

    ΔX.sub.2 =f×α.sub.2 ×ΔT

When ΔX₁ =ΔX₂, the laser beam emitted from the collimating lens 24 canbe kept parallel, even if a temperature variation occurs. In order tomake the deviation amount ΔX₁ equal to the deviation amount ΔX₂, i.e.ΔX₁ =ΔX₂, it is necessary to construct a lens system which satisfies thefollowing equation:

    α.sub.1 -β.sub.1 /(n-1)=α.sub.2

For example, in the case of BK 7, a typical glass material for opticalglass, n is 1.5163, α₁ is 7.4×10⁻⁶, and β₁ is 2.8×10⁻⁶.

Hence, in order to continue to project a laser beam from a single lensmade of BK 7 as a parallel light beam regardless of temperature changes,it is necessary to employ a lens holding member, which holds the abovesingle lens, having the following coefficient of linear expansion α₂ :

    α.sub.2 =α.sub.1 -β.sub.1 /(n-1)=1.98×10.sup.-6.

It is noted that the coefficient of linear expansion α₂ of aluminum,which is often used for making the lens holding member, is 23.6×10⁻⁶.

The coefficient of linear expansion of glass is generally smaller thanthat of the metal used for the lens holding member, and the temperaturecoefficient of refractive index of glass is often a negative value. Forthis reason, the back focal distance of an ordinary designed lens variesvery little, whereas the lens holding member shrinks or expands by alarge amount, thereby the diverging or converging state of the laserbeam emitted from the lens, held by the lens holding member, varies dueto temperature variations.

In order to solve this problem, according to the present invention, thelens, held by the lens holding member, is designed so as to vary itsback focal distance by an amount corresponding to the amount the lensholding member varies due to temperature variations, based on the factthat the temperature coefficient of refractive index varies depending onthe type of glass. Specifically, the collimating lens 24 is designedsuch that the positive lens used in the collimating lens 24 is made of aglass material having a small temperature coefficient of refractionindex (or having a temperature coefficient of refraction index of alarge negative value) and that the negative lens used in the collimatinglens 24 is made of a glass material having a large temperaturecoefficient of refraction index, which makes it possible for thecollimating lens to vary its back focal distance in a wide range. Thefollowing conditional formula 1-1 refers to the temperature correctioncondition:

    Δn.sub.c- -Δn.sub.c+ >5.0×10.sup.-6 /°C.1-1

wherein,

Δn_(c+) represents the temperature coefficient of refractive index ofthe positive lens, in the collimating lens 24, which has the largestpositive power among all the positive lenses in the collimating lens 24;

Δn_(c-) represents the temperature coefficient of refractive index ofthe negative lens, in the collimating lens 24, which has the largestnegative power among all the negative lenses in the collimating lens 24.

In the case where, in the above formula 1-1, the difference (Δn_(c-)-Δn_(c+)) is equal to or smaller than the condition (5.0×10⁻⁶ /°C.), thenumber of lenses in the collimating lens 24 must be increased, or apositive lens or negative lens of considerably stronger power, incomparison with the total power of the collimating lens 24, must beused. Therefore, the condition that the difference (Δn_(c-) -Δn_(c+)) isequal to or smaller than the condition (5.0×10⁻⁶ /°C.) is unsuitable formaking a high precision collimating lens 24.

It is preferable that the chromatic aberration of the collimating lens24 be corrected, so as not to be affected by changes in the wavelengthof the laser beam emitted from the laser diode 23. The followingconditional formula 1-2 refers to the chromatic aberration correctioncondition:

    ν.sub.c+ /ν.sub.c- >2.0                              1-2

wherein,

ν_(c+) represents the Abbe number of the positive lens, in thecollimating lens 24, which has the largest positive power among all thepositive lenses in the collimating lens 24; and,

ν_(c-) represents the Abbe number of the negative lens, in thecollimating lens 24, which has the largest negative power among all thenegative lenses in the collimating lens 24.

If the above formula, 1-2 is not satisfied, the chromatic aberration ofthe collimating lens 24 would not be able to be corrected withoutincreasing the number of lenses in the collimating lens 24, which is notpreferable for making the collimating lens 24 since the behavior of thelenses, due to temperature changes, will be even more complicated.

The occurrence of variation in the diverging or converging state of thelaser beam emitted from the collimating lens 24, can be prevented, evenif the wavelength of the laser diode 23 changes due to a temperaturevariation, by way of selecting a particular glass material whichsatisfies both the above formulae 1-1 and 1-2 and also by selecting asuitable power distribution for the collimating lens 24, i.e. selectinga suitable power distribution for each lens in the collimating lens 24.

According to the first embodiment to which the second aspect of thepresent invention is applied, chromatic aberration of the beam expanderB (i.e. beam diameter changing optical system) is also correctedchromatic aberration, independent from the collimating lens 24. The beamexpander B may be constructed by disposing two positive lens groups withthe focal points thereof being coincident with each other. However, itis preferable that the beam expander B be comprised of a positive lensgroup and a negative lens group. The magnification of the beam expanderB in this first embodiment is not so large, thus the beam expander B iscomprised of a positive lens element and a negative lens element.

In order to further extend the beam projecting distance, one could makethe diameter of the projected laser beam large, by means of enlargingthe magnification of the beam expander B. To achieve this, it ispreferable for each of the positive and negative lens groups, of thebeam expander B, to be comprised of more than one lens. In order toprovide a low cost beam expander B, it is preferable for the beamexpander B to be comprised of one positive lens and one negative lens,and for it to satisfy the following conditional formula 1-4. Note, thatit is unsuitable to apply the following conditional formula 1-4 to abeam expander B having more than one positive lens or more than onenegative lens.

    0.6<|(f.sub.b- -ν.sub.b+)/(f.sub.b+ ×ν.sub.b-)|<1.2                         1-4

wherein:

f_(b-) represents the focal length of the negative lens;

ν_(b-) represents the Abbe number of the negative lens;

f_(b+) represents the focal length of the positive lens; and

ν_(b+) represents the Abbe number of the positive lens.

The above conditional formula 1-4 refers to the condition of chromaticaberration correction of the beam expander B. If the value |(f_(b-)×ν_(b+))/(f_(b+) ×ν_(b-))| is outside of the range defined by formula1-4, the degree of divergence or convergence of the laser beam, emittedfrom the beam expander B, changes due to the chromatic aberration of thebeam expander B, in the case where the chromatic aberration of thecollimating lens 24 has already been corrected.

The beam expander B may be designed so as to nullify any effect causedby a contraction or expansion thereof due to a temperature change, likethe above-noted collimating lens 24. However, when the beam expander Bhas two lens groups comprising of a positive lens and a negative lens,as noted above, no major problems would arise if the beam expander B wasdesigned without any consideration being given as to the temperatureeffects on the beam expander B. The reason for this is that the effectof variations in temperature on the beam expander, have a much smallereffect on the degree of divergence or convergence of a laser beam, thando the effects of temperature variation on the collimating lens 24.

FIG. 15 illustrates a first embodiment of a collimating lens arrangementto which the second aspect of of the present invention is applied. Thecollimating lens 24 is provided with lenses L101, L102, L103 and L104,and has a focal length of 6 mm. Lenses L101 and L102 are bonded L105 isthe cover glass of the laser diode 23, r1 to r9 indicate the radius ofcurvature of the cover glass and each lens surface, and d1 to d8indicate the cover glass thickness, the lens thickness or the distancebetween the lenses.

The cover glass L105, lenses L104, L103, L102 and L101 are made of thefollowing glass materials--BSL 7, LAL 18, LAL 13, PBH 53 and PHM 52,respectively (these are the names of glass materials produced by theJapanese company, "Ohara Kabushikigaisha").

Table 1 shows numerical data regarding the first embodiment of thecollimating lens 24, to which the second aspect of the present inventionis applied. In Table 1, as well as in the following tables, "Ri"designates the radius of curvature of the i-th lens surface counted fromthe light source side, "Di" the thickness of the i-th glass cover or thelens or the distance between the lenses from the light source side, "n"the refractive index of the lens at a wavelength of 635 nm, "ν" is theAbbe number of the lens at the d-line thereof, "Δn" is the temperaturecoefficient of refractive index of the lens at the C line thereof andits unit is 10⁻⁶ /°C.

FIGS. 16 to 18 show the longitudinal aberrations, the transversalaberrations and the wavefront aberrations, respectively. The aberrationsare those on the image forming surface when light is incident thereonfrom the right side in FIG. 15. When the collimating lens 24 is used,the semiconductor laser 23 is placed on the left, as viewed in FIG. 15.In the drawings, a solid line "SA" designates spherical aberration, adotted line "SC" the sine condition, "W" the angle of view, a solid line"S" an astigmatism in the sagittal plane, a dotted line "M" anastigmatism in the meridional plane. A solid line (not the solid linesshowing "SA" and "S") designates a wavelength of 635 nm. The smalldotted line designates a wavelength of 625 nm. The large dotted linedesignates a wavelength of 645 nm.

                  TABLE 1                                                         ______________________________________                                        Face No. Ri         Di     n       ν Δ n                             ______________________________________                                        1        ∞    0.30   1.51455 64.1 2.7                                   2        ∞    2.73                                                      3        -4.624     1.80   1.72623 54.7 3.9                                   4        -3.519     0.10                                                      5        -75.123    1.80   1.69065 53.2 5.2                                   6        -7.118     4.38                                                      7        -105.190   1.60   1.83928 23.9 11.1                                  8        8.483      2.25   1.61586 63.4 -3.6                                  9        -13.310    -                                                         ______________________________________                                    

FIG. 19 shows an example of a lens arrangement of the beam expander Bused together with the collimating lens 24 having the characteristicsshown in Table 1. The beam expander B is comprised of a front lenselement 31 and a rear lens element 32, and has a beam magnification of1.3.

The front lens element 31 is constructed from PBM5 and the rear lenselement 32 of LAL 13 (these are the names of glass materials produced bythe above noted Japanese company, "Ohara Kabushikigaisha").

Table 2 shows numerical data regarding the above beam expander B havingthe characteristics shown in Table 1.

FIGS. 20 to 22 show the longitudinal aberrations, the transversalaberrations, and the wavefront aberrations, respectively. Theaberrations are those on the image forming surface when light isincident thereon from the left side of FIG. 19. In the drawings "ER"designates entrance pupil height, "B" the incident angle, "S" thesagittal plane, and "M" the meridional plane.

                  TABLE 2                                                         ______________________________________                                        Face No. Ri        Di      n       ν Δ n                             ______________________________________                                        1        -59.000   2.50    1.60003 38.0 2.8                                   2        237.849   23.09                                                      3        ∞   3.50    1.69065 53.2 5.3                                   4        -72.480   --                                                         ______________________________________                                    

The first embodiment to which the second aspect of the present inventionis applied has been described, in which both the collimating lens 24 andthe beam expander B are designed so as to correct the chromaticaberration thereof.

In the second embodiment to which the second aspect of the presentinvention is applied, the collimating lens 24 is not designed to becompletely corrected from chromatic aberration. Instead, the variationoccurring in the laser beam emitted from the collimating lens 24 due totemperature change, is corrected by the collimating lens 24 itself,while the total chromatic aberration of the collimating lens 24 and thebeam expander B is corrected by the overall optical system including thecollimating lens 24 and the beam expander B.

It is also required in this second embodiment of the present inventionthat the collimating lens 24 satisfies the above conditional formula 1-1for correcting temperature variation. Since it is preferable that a lotof chromatic aberration should not remain in the overall optical system,including the collimating lens 24 and the beam expander B, for the beamexpander B to have a simple structure, it is thus preferable that thesecond embodiment should also satisfy the following formula 1-3, similarto the above-noted formula 1-2:

    ν.sub.c+ /ν.sub.c- >2.0                              1-3

wherein,

ν_(c+) represents the Abbe number of the positive lens, in thecollimating lens 24, which has the largest positive power among all thepositive lenses in the collimating lens 24; and

ν_(c-) represents the Abbe number of the negative lens, in thecollimating lens 24, which has the largest negative power among all thenegative lenses in the collimating lens 24.

When the collimating lens 24, satisfying the formula 1-3 is used, thebeam expander B has its chromatic aberration in the range defined by thefollowing formula 1-5:

    0.4<|(f.sub.b- ×ν.sub.b+)/(f.sub.b+ ×ν.sub.b-)|<2.0                         1-5

wherein:

f_(b-) represents the focal length of the negative lens of the beamexpander B,

ν_(b-) represents the Abbe number of the negative lens of the beamexpander B,

f_(b+) represents the focal length of the positive lens of the beamexpander B, and

ν_(b+) represents the Abbe number of the positive lens of the beamexpander B.

In this second embodiment, the reason why the beam expander B isdesigned to correct only that part of the chromatic aberration occurringin the collimating lens 24, and corrects none of the variationoccurring, due to temperature change, in both the collimating lens 24and the beam expander B, is that the wavelength of the laser beamemitted by the laser diode 23 varies in the same way at any point alongthe laser beam, whereas the temperature may be different between thecollimating lens 24, which is disposed close to the laser diode 23 (aheat source), and the beam expander B, which is disposed away from thelaser diode 23.

FIG. 23 shows a first example of a collimating lens arrangement of asecond embodiment to which the second aspect of the present invention isapplied. Numerical data regarding this collimating lens 24 is shown inTable 3. Longitudinal aberrations, transversal aberrations and wavefrontaberrations are shown in FIGS. 24 to 26, respectively. The cover glassL105 is made of BSL7, and lenses L104, L103, L102 and L101 are made ofLAL 18, LAL 13, PBH 6 and FPL 51, respectively.

                  TABLE 3                                                         ______________________________________                                        Face No. Ri        Di     n       ν Δ n                              ______________________________________                                        1        ∞   0.30   1.51455 64.1 2.7                                    2        ∞   2.65                                                       3        -4.350    1.80   1.72623 54.7 3.9                                    4        -3.476    0.10                                                       5        -59.281   1.80   1.69065 53.2 5.2                                    6        -6.913    4.38                                                       7        178.091   1.60   1.79856 25.4 9.0                                    8        9.253     2.25   1.49566 81.6 -5.5                                   9        -11.404   --                                                         ______________________________________                                    

FIG. 27 shows an example of a lens arrangement of the the beam expanderB used together with the collimating lens 24 having the characteristicsshown in Table 3. The beam expander B has a beam magnification of 1.80.

The front lens group 31 consists of a negative lens element, constructedfrom TIH 53, and the rear lens group 32 consists of a positive lenselement of FPL 51.

Table 4 shows numerical data regarding the above beam expander B usedtogether with the collimating lens 24 having the characteristics shownin Table 3.

FIGS. 28 to 30 show the longitudinal aberrations, the transversalaberrations, and the wavefront aberrations, respectively.

                  TABLE 4                                                         ______________________________________                                        Face No.  Ri       Di        n     ν   Δ n                           ______________________________________                                        1         -226.334 2.50      1.83925                                                                             23.8     1.4                               2         41.595   30.86                                                      3         302.150  3.80      1.49566                                                                             81.6   -5.5                                4         -42.213  --                                                         ______________________________________                                    

FIG. 31 shows a second example of a collimating lens arrangement of thesecond embodiment to which the second aspect of the present invention isapplied. Numerical data regarding this collimating lens 24 is shown inTable 5. Longitudinal, transversal and wavefront aberrations are shownin FIGS. 32 to 34, respectively.

Cover glass L105 is made of BSL 7, and lenses L104, L103, L102 and L101are made of LAL 13, LAL 14, PBH 53 and FPL 52, respectively.

                  TABLE 5                                                         ______________________________________                                        Face No. Ri        Di     n       ν Δ n                              ______________________________________                                        1        ∞   0.30   1.51455 64.1 2.7                                    2        ∞   2.65                                                       3        -4.347    1.80   1.69065 53.2 5.2                                    4        -3.432    0.10                                                       5        -60.570   1.80   1.69404 55.5 3.8                                    6        -6.964    4.38                                                       7        55.474    1.60   1.83928 23.9 11.1                                   8        9.605     2.25   1.45488 90.3 -5.3                                   9        -10.909   --                                                         ______________________________________                                    

FIG. 35 shows an example of a lens arrangement of the beam expander Bused together with the collimating lens 24 having the characteristicsshown in Table 5. Numerical data regarding this beam expander B is shownin Table 6. Longitudinal, transversal and wavefront aberrations areshown in FIGS. 36 to 38, respectively. Beam magnification of the beamexpander B is fixed at 2.07. The front lens group 31 is made of TIH 53and the rear lens group 32 is made of FPL 52.

                  TABLE 6                                                         ______________________________________                                        Face No.  Ri       Di        n     ν   Δ n                           ______________________________________                                        1         166.594  2.50      1.83925                                                                             23.8     1.4                               2         25.516   36.37                                                      3         -1170.933                                                                              3.80      1.45488                                                                             90.3   -5.3                                4         -33.184  --                                                         ______________________________________                                    

FIG. 39 shows a third example of a collimating lens arrangement of thesecond embodiment to which the second aspect of the present invention isapplied. Numerical data regarding the collimating lens 24 is shown inTable 7. Longitudinal, transversal and wavefront aberrations are shownin FIGS. 40 to 42, respectively.

Cover glass L105 is made of BSL 7, and lenses L104, L103, L102 and L101are made of LAL 7, PHM 51, TIH 6 and FPL 51, respectively.

                  TABLE 7                                                         ______________________________________                                        Face No. Ri        Di     n       ν Δ n                              ______________________________________                                        1        ∞   0.30   1.51455 64.1 2.7                                    2        ∞   2.53                                                       3        -4.619    1.80   1.64915 5.85 2.0                                    4        -3.177    0.10                                                       5        -44.949   1.80   1.61484 62.8 -0.8                                   6        -6.906    4.38                                                       7        81.307    1.60   1.79857 25.4 0.8                                    8        9.511     2.25   1.49566 81.6 -5.5                                   9        -11.372   --                                                         ______________________________________                                    

FIG. 43 shows an example of a lens arrangement of the beam expander Bused together with the collimating lens 24 having the characteristicsshown in Table 7. Numerical data regarding this beam expander B is shownin Table 8. Longitudinal, transversal and wavefront aberrations areshown in FIGS. 44 to 46, respectively. Beam magnification of the beamexpander B is fixed at 1.70.

The front lens group 31 is made of TIH 6 and the rear lens group 32 ismade of FPL 52.

                  TABLE 8                                                         ______________________________________                                        Face No.  Ri       Di        n     ν   Δ n                           ______________________________________                                        1         88.796   2.50      1.79857                                                                             25.4     0.8                               2         29.160   39.79                                                      3         -122.664 3.80      1.45488                                                                             90.3   -5.3                                4         -32.265  --                                                         ______________________________________                                    

FIG. 47 shows a fourth example of a collimating lens arrangement of thesecond embodiment to which the second aspect of the present invention isapplied. Numerical data regarding this collimating lens 24 is shown inTable 9. Longitudinal, transversal and wavefront aberrations are shownin FIGS. 48 to 50, respectively.

Cover glass L105 is made of BSL 7, and the lenses L104, L103, L102 andL101 are made of LAL 13, LAL 14, PBH 71 and PHM 52, respectively.

                  TABLE 9                                                         ______________________________________                                        Face No. Ri         Di     n       ν Δ n                             ______________________________________                                        1        ∞    0.30   1.51455 64.1 2.7                                   2        ∞    2.43                                                      3        -4.318     1.80   1.69065 53.2 5.2                                   4        -3.372     0.10                                                      5        -25.326    1.80   1.69404 55.5 3.8                                   6        -6.002     4.38                                                      7        -183.086   1.60   1.91390 21.3 11.8                                  8        9.821      2.25   1.61586 63.4 -3.6                                  9        -11.797    --                                                        ______________________________________                                    

FIG. 51 shows an example of a lens arrangement of the beam expander Bused together with the collimating lens 24 having the characteristicsshown in Table 9. Numerical data regarding this beam expander B is shownin Table 10. Longitudinal, transversal and wavefront aberrations areshown in FIGS. 52 to 54, respectively. Beam magnification of the beamexpander B is fixed at 1.33.

The front lens group 31 is made of BAL 15 and the rear group 32 is madeof PBL 25.

                  TABLE 10                                                        ______________________________________                                        Face No. Ri        Di      n       ν Δ n                             ______________________________________                                        1        -68.751   2.50    1.55463 58.7 2.6                                   2        121.059   23.37                                                      3        330.562   3.50    1.57838 40.7 2.5                                   4        -74.023   --                                                         ______________________________________                                    

FIG. 55 shows an example of the lens system consisting of thecollimating lens 24, having the above first example of a collimatinglens arrangement usable in the second embodiment to which the secondaspect of the present invention is applied, and the beam expander Bshown in FIG. 27. Numerical data regarding this combined lens system isshown in Table 11. Longitudinal aberration is shown in FIG. 56. Thiscombined lens system functions to effectively correct the chromaticaberration thereof. Similar effective functions can be expected in theother four lens examples, i.e. in the first embodiment to which thesecond aspect of the present invention is applied, the second, third andfourth lens arrangements of the second embodiment to which the secondaspect of the present invention is applied.

                  TABLE 11                                                        ______________________________________                                        Face No.  Ri       Di        n     ν   Δ n                           ______________________________________                                        1         ∞  0.30      1.51455                                                                             64.1   2.7                                 2         ∞  2.65                                                       3         -4.350   1.80      1.72623                                                                             54.7   3.9                                 4         -3.476   0.10                                                       5         -59.281  1.80      1.69065                                                                             53.2   5.2                                 6         -6.913   4.38                                                       7         178.091  1.60      1.79856                                                                             25.4   9.0                                 8         9.253    2.25      1.49566                                                                             81.6   -5.5                                9         -11.404  20.00                                                      10        -226.334 2.50      1.83925                                                                             23.8   1.4                                 11        41.595   30.86                                                      12        302.150  3.80      1.49566                                                                             81.6   -5.5                                13        -42.213  --                                                         ______________________________________                                    

Table 12 shows respective values derived from the conditional formula1-1 in Examples 1 to 5, corresponding to the first embodiment, thefirst, second, third, and fourth lens arrangements of the secondembodiment, to which the second aspect of the present invention isapplied.

Table 13 shows respective values derived from the conditional formulae1-2 and 1-3 in Examples 1 to 5 corresponding to the first embodiment,the first, second, third, and fourth lens arrangements of the secondembodiment, to which the second aspect of the present invention isapplied.

Table 14 shows respective values derived from the conditional formulae1-4 and 1-5 in Examples 1 to 5 corresponding to the first embodiment,the first, second, third, and fourth lens arrangements of the secondembodiment, to which the second aspect of the present invention isapplied.

Respective values derived from the conditional formula 1-5 in Examples 1to 5 are the same as those derived from the conditional formula 1-4;only the figure ranges are different between the formulae 1-4 and 1-5.

                  TABLE 12                                                        ______________________________________                                        formula 1-1: Δn.sub.c-  - Δn.sub.c+  > 5.0 × 10.sup.-6      /° C.                                                                          Δn.sub.c+                                                                          Δn.sub.c-                                                                      Δn.sub.c-  - Δn.sub.c+                  ______________________________________                                        Example 1 -3.70        11.20  14.90                                           Example 2 -5.60        10.00  15.60                                           Example 3 -5.40         9.10  14.50                                           Example 4 -5.60        1.0     6.60                                           Example 5 -3.60        12.0   15.60                                           ______________________________________                                    

                  TABLE 13                                                        ______________________________________                                        formulae 1-1 and 1-2: ν.sub.c+ /ν.sub.c-  > 2.0                                  ν.sub.c+                                                                              ν.sub.c-                                                                          ν.sub.c+ /ν.sub.c-                           ______________________________________                                        Example 1  63.4         23.9   2.65                                           Example 2  81.6         25.4   3.21                                           Example 3  90.3         23.9   3.78                                           Example 4  81.6         25.4   3.21                                           Example 5  63.4         21.3   2.98                                           ______________________________________                                    

                  TABLE 14                                                        ______________________________________                                        formula 1-4: 0.6 < | (f.sub.b-  × ν.sub.b+)/(f.sub.b+       × ν.sub.b-) | < 1.2                                         formula 1-5: 0.4 < | (f.sub.b-  × ν.sub.b+)/(f.sub.b+       × ν.sub.b-) | < 2.0                                                                              |(f.sub.b-  ×                                                  ν.sub.b+ /                            f.sub.b+     ν.sub.b+                                                                           f.sub.b-  ν.sub.b-                                                                         (f.sub.b+  × ν.sub.b-).vertl                                         ine.                                     ______________________________________                                        Example 1                                                                             -78.537  38.0    104.945 53.2  0.9544                                 Example 2                                                                             -41.690  23.8    74.999  81.6  0.5247                                 Example 3                                                                             -36.194  23.8    75.000  90.3  0.5462                                 Example 4                                                                             -55.401  25.4    94.998  90.3  0.4823                                 Example 5                                                                             -78.689  58.7    104.899 53.2  1.9224                                 ______________________________________                                    

FIG. 57 shows the variation of the beam diameter, due to temperaturevariation, of the laser beam emitted from the lens system consisting ofthe collimating lens 24 and the beam expander B according to the abovefirst embodiment to which the second aspect of the present invention isapplied.

FIG. 58 shows the variation of the beam diameter, due to temperaturevariation, of the laser beam emitted from the lens system consisting ofthe collimating lens 24 and the beam expander B according to the firstlens arrangement of the second embodiment to which the second aspect ofthe present invention is applied.

As is apparent from FIGS. 57 and 58, the beam diameter of the laser beamat a long distance (at a distance of 200 meters ahead in FIGS. 57 and58) is maintained constant by an effective correcting function in eachof the respective lens structures described above, in spite of theoccurrence of temperature variation, as compared with the case wherethere is no correction for temperature variation.

As can be seen from the foregoing, according to the present invention, abeam projecting device can be provided that is capable of scanning anobject with a sufficiently small beam spot from a short distance to along distance, without any focusing operation necessary for making asmall beam spot, in spite of the occurrence of temperature variation.

Another embodiment of the present invention for measuring the radius ofcurvature R of the wavefront of the laser beam and controlling the beamwaist position, will now be explained. The basic principle of theinvention will be explained below.

A gist of the present invention is that the beam waist position of theprojected laser beam (e.g. Gaussian beam) can be determined simply if abeam diameter at any distance (in the case of the present embodiment,the diameter of the laser beam at a beam projection opening of arotatable laser projector 11 of the projecting apparatus, from which thebeams are projected) and a radius of curvature R of the beam wavefrontare known. Consequently, if the radius of curvature R of the beamwavefront has been detected by a predetermined means, the beam waistposition is determined, since the projecting beam diameter is initiallyobtained according to a performance specification of the projectionapparatus.

In a laser beam (Gaussian beam) in general, when the beam diameter atthe beam waist position is W₀, the beam diameter at a portion away fromthe beam waist position by the distance X is W, the radius of curvatureof the wavefront at the position (X) is R and the wavelength of thelaser beam is λ, it is known that the beam diameter W and the wavefrontradius of curvature R are expressed by the following equations (refer to"Introduction to Image-forming Optics" written by Yoshiya Matsui, page112 to 115, published by Keigaku Shuppan):

    W=W.sub.0 {1+(4λX/πW.sub.0.sup.2).sup.2 }.sup.1/2 2-1

    R=X{1+(πW.sub.0.sup.2 /4λX).sup.2 }              2-2

These equations can be rewritten as shown below:

    W.sub.0 =W{1+(πW.sup.2 /4λR).sup.2 }.sup.-1/2    2-3

    X=R{1+(4λR/πW.sup.2).sup.2 }.sup.-1              2-4

When the type of laser projection apparatus is specified, the laser beamwavelength and the beam diameter W, of the projecting beam at aprojecting opening of the laser projection apparatus will be determined.Consequently, after calculating the radius of curvature R of thewavefront of the laser beam, it is possible to determine the beam waistdiameter W₀ at the beam waist position by the equation 2-3, and thedistance between the laser projecting apparatus and the beam waist bythe equation 2-4. FIG. 70 shows the relationship between the wavefrontradius of curvature R and the beam waist distance X, when the beamdiameter W at the projecting opening at the projecting device is takenas a parameter. As shown in the figure, the radius of curvature R of thewavefront determines the beam waist distance X.

There are two ways for detecting the value corresponding to thewavefront radius of curvature R, namely:

(1) by directly detecting the wavefront radius of curvature R; and,

(2) by collecting beams with the wavefront radius of curvature R by alens, and then detect and observe the collective state of the lens.

For instance, a radial shear interferometer is used for (1), and a focuserror detecting optical system with the astigmatism method, which isadopted in a conventional optical disk apparatus, is used for (2).

In the first embodiment to which the third aspect of the presentinvention is applied, the feature of the third aspect resides in theprocess of calculation of the beam waist diameter W₀ and the beam waistdistance X by measuring the radius of curvature R of the wavefront,which is obtained at the time of determining the laser beam diameter Wprojected from the projecting opening. Explanations will be givenaccording to FIGS. 59 through 64.

FIG. 59 shows the first embodiment of the third aspect. The laserprojection apparatus is arranged to measure the wavefront radius ofcurvature R of the projected laser beam, by a focus error detectionmeans with the astigmatism method according to method (2) mentionedabove. The laser projecting apparatus has a laser projecting portionincluding a means for adjusting the beam waist position of theprojecting laser beam. The laser projecting portion includes a laserlight source 101 and a rotatable laser projector 111 which is rotatedabout a rotational axis 111c coincident with the axis of the laser beamemitted from the laser light source 101 while projecting the laser beamin the direction substantially normal to the rotational axis 111c.Furthermore, the laser projecting apparatus includes a focus errordetecting system 121 as means for detecting the radius of curvature R ofthe wavefront. The focus error detecting system 121, which is normallyused in an optical disc device, is designed to receive a branched laserbeam, which is branched from the laser beam emitted from the laser lightsource 101, and to calculate the radius of curvature R of the wavefront.Moreover, the laser projecting apparatus includes a controller 131,which is arranged to adjust a position of the beam waist BW (distance X)in accordance with the focus error signal issued from the focus errordetecting circuit 121.

The laser light source 101 is provided with a semiconductor laser 102, acollimating lens 103 for converting the laser beam, projected from thesemiconductor 102, substantially parallel, and a beam splitter 104through which a major part of the parallel laser beam (about 90%)passes, the rest being reflected in a direction towards the focus errordetection system 121. The rotatable laser projector 111 is rotatablydriven around the rotational axis 111c by a drive mechanism (not shown).The optical axis of the collimating lens 103 coincides with therotatable axis 111c. That is, the laser beam emitted from the laserlight source 101 progresses along the rotational axis 111c, of therotatable laser projector 111, before being reflected in the directionperpendicular to the rotatable axis 111c by means of a first mirror 112and a second mirror 113, the surfaces of which are oriented to form anangle of 45 degrees. The radius of curvature of the wavefront and thediameter of the laser beam, which is being projected, are defined as theradius of curvature R of the wavefront and the beam diameter W.

The collimating lens 103 is movable in the direction parallel to anoptical axis of the collimating lens 103. Due to such a movement of thecollimating lens 103, the distance d, between the semiconductor laser102 and the collimating lens 103 varies, the wavefront curvature radiusR of the laser beam accordingly varies, thus resulting in variations ofthe beam waist BW. Consequently, the beam waist distance X and the beamwaist diameter W₀ are varied.

The laser beam projected from the rotatable laser projector 111 has thebeam waist BW and the beam waist diameter W₀, at a predetermineddistance X away from the rotatable beam projector. When the opticalcomponents of the laser light projecting apparatus are manufactured withhigh precision, the distance X of the beam waist BW and the wavefrontcurvature radius R of the laser beam projected from the laser lightprojection apparatus, is determined, primarily, only by the distance dbetween the semiconductor laser 102 and the collimating lens 103.

On the other hand, the laser beam reflected at the beam splitter 104 isconverged on the converging lens 122, goes through a cylindrical lens123, and the laser beam is finally converged onto a divided sensor 124,in which the sensor is segmented in four sections. The cylindrical lens123 is positioned so that the lens 123 has a refraction power in thedirection perpendicular to the sheet of FIG. 59, and has no refractionpower in the direction parallel to the sheet of FIG. 59. The sensor 124is formed in a cross shape. The four segments of the sensor 124 areformed by perpendicularly crossing lines. The crossing lines are sopositioned that these lines makes the angle of 45 degrees with the alongitudinal axis (parallel to the sheet of FIG. 59) representing thedirection of the generating line of the cylindrical lens 123. Usually,the longitudinal axis represents the center of curvature of acylindrical lens of this type. When the radius of curvature R of thewavefront varies, the shape of a beam spot formed by the laser beamconverged on the sensor 124 is accordingly transformed, e.g. from anellipse to a circle, or to another ellipse having a different posturefrom the first ellipse. In accordance with the variation of the beamspot shapes, the light receiving amount of the sensor 124 varies, andthus the output of each segment of the sensor 124 varies.

The output from each segment of the sensor 124 is amplified in aprocessing portion 132, belonging to the control portion 131, and isused for predetermined arithmetic operations in a microcomputer 133. Themicrocomputer 133 displays the calculated wavefront curvature radius Rand beam waist distance X, on a display 134. The microcomputer 133calculates or determines a shifting amount and a shifting direction forshifting the beam waist position to a specific position in accordancewith the radius of curvature R of a wavefront and the beam waistdistance x and thereafter actuates the lens driving mechanism 105through the controller portion 135 to shift the collimating lens 103 tothe above-noted specific direction in accordance with the abovecalculated results of shifting amount and shifting direction. Thisshifting operation makes it possible to maintain the beam waist distancex against disturbance such as temperature change, wavelength change,etc. or to form the beam waist at any desired position.

By a manual input portion 136, operational options, such as whether ornot to maintain or vary the distance X, can be manually selected. Themanual input portion 136 is also capable of setting and selectingvarious data, such as a predetermined distance X. The manual inputportion 136 is also capable of programming an operation process inadvance, and of using those measurements, under a predetermined mode,instantly when the ON button is pushed. Some of the operations describedabove can be carried out by a remote controller 141, separately arrangedfrom the control portion 131. An output signal from the remotecontroller 141 is received by a receiving portion 137 and is inputted tothe microcomputer 133, through the input portion 136. The signal fromthe remote controller 141 is transferred to the receiving portion 137through wire, infrared rays, electric or ultra-sound waves.

Now that an outline of the embodiment has been explained, the structureand operation of the focus error detecting system 121 will be explainedwith reference to FIGS. 60 and 61. FIG. 60 shows an outline of themeasurement process of the focus error detecting circuit 121.

The focus error detecting system 121 according to this embodiment isprovided with an optical system equivalent to a focus error detectionoptical system using the astigmatism method, which has been used in anoptical disc device. The sensor 124 is provided with four segmentshaving sensors 1241, 1242, 1243 and 1244, divided by crossing lines. Thelaser beam reflected by the beam splitter 104 in the direction of theconverging lens 122, is converged by the converging lens 122 and thecylindrical lens 123 at the crossing point O, substantially at thecenter of the sensor 124. The sum of the outputs of the sensors 1241 and1243 placed diagonally, minus the sum of the outputs of the sensors 1242and 1244 also arranged diagonally creates the focus error signal (FES).Outputs S₁, S₂, S₃ and S₄ of respective sensors 1241, 1242, 1243 and1244, can be formed in the following equation:

    FES=(S.sub.1 +S.sub.3)-(S.sub.2 +S.sub.4)

According to the size of the wavefront curvature radius R of the laserbeam, incident on the focus error detecting circuit 121, the size of thefocus error signal FES changes. This operation will be explained withreference to the focus error detection circuit in comparison with theoptical disc device.

Assuming a case where a light spot emitted from an objective lens 152 isfocused on an information recording surface 151 of an optical disc (notshown) with no deviation (i.e. information recording surface 151_(B)shown in FIG. 60), the spot diameter is smallest. In this case, a light,reflected on the surface 151_(B) and being incident on the focus errordetecting circuit 121, is made parallel, like light B. Consequently, theradius of curvature R_(B) of the wavefront of the light B is madeinfinity. At this time, the light spot on the sensor 124 is madecircular as shown with a letter B on the drawing, and the focus errorsignal FES becomes zero.

When the information recording surface 151 is apart from the objectivelens 152 by the distance Δ, the light beam reflected from theinformation recording surface 151_(A), to be incident on the focus errordetection system, becomes a laser beam as shown by symbol A with aradius of curvature R_(A). A light spot on the sensor 124 becomes anellipse, as shown by symbol A', having a long axis coincident with thediagonal lines of the segmented sensors 1241, 1243, thus the focal errorsignal calculated by the above equation becomes a plus value.

When the information recording surface 151 is away from the objectivelens 152 by a distance Δ, the beam reflected on the informationrecording surface 151_(C), to be incident on the focus error detectioncircuit 121, forms a laser beam as shown by symbol C, obtaining awavefront radius of curvature R_(C) of the light beam C. The light spoton the sensor 124 has, as shown by symbol C', an ellipse with its longaxis perpendicular to the light spot A' and the focus error signalFES={(S₁ +S₃)-(S₂ +S₄)} has a minus value.

According to the optical disc device, the objective lens isservo-controlled and is constantly focussed on the optical disc in orderto make the focus error signal FES zero, i.e. the wavefront radius ofcurvature R_(B) is controlled to make an in-focus state on the disc.

As described above, the size of shift or off-set value Δ between theinformation recording surface 151 and a focal point of the objectivelens 152 changes the wavefront R of the light beam incident on the focuserror detecting circuit and the shape of the light spot formed on thesensor 124, so that the focus error signal FES is generated. It can beaccordingly said that the focus error detecting system 121 detects theradius of curvature of the wavefront of the laser beam incidentthereupon.

The size of the focus error signal FES varies according to a defocusvalue, to thereby obtain an S curve as shown in FIG. 61. The S curveshows the relation between the shift value Δ (defocus value), betweenthe information recording surfaces of the optical disks 151_(A),151_(B), and the focal point of the objective lens 152 of the focallength f₀, and the size of the focus error signal FES obtained. B inFIG. 60 shows the light beam (the input wavefront) obtained when theoptical disc 151_(B) is placed in an in-focus state. A and C, also inFIG. 60, show the beam (the input wavefront) when the informationrecording surfaces of the optical discs 151_(A), 151_(C) are placed inan out-of-focus state. The focus error signal FES becomes the pointO_(B) in the case of the light beam B, and the point O_(A) in the caseof the light beam A. That is, when the size of the focus error signalFES is determined, it is easy to determine the shift value Δ. It is alsoeasy to design or determine the change of the focus error signal FEScorresponding to the shift value or range of the straight line zero ofthe S curve, and sensitivity about the point O_(B), by making an opticalsystem of focus error detecting circuit more suitable. According to theembodiment, a spot of the light beam B on the sensor 124 having the foursegments of the sensor becomes circular as shown by symbol B' with theFES=0. However, it is easy to set FES=0 when the light beam A occurs. Itis equivalent to the case that FES equals zero when the wavefrontcurvature radius is R_(A).

The relation between the shift value Δ and the wavefront radius ofcurvature R is given by the following equation:

    R=f.sub.0.sup.2 /2Δ(f.sub.0 >>Δ)               2-5

Although the S curve in the focus error detecting circuit is to show therelation between the shift value Δ and the focus error signal FES, withthe use of the above equation 2-5, it can be said that the wavefrontradius of curvature R of light beam being incident on the focus errordetection circuit is also simultaneously detected. Namely, If theobjective lens has a focal point f₀, under a set of predeterminedconditions (a detecting sensitivity, and so forth) of the correspondingfocus-error detecting circuit, the focus error signal FES, correspondingto the shift value Δ (change of wave face curvature radius R), will beobtained. The laser projection apparatus, in use, does not have theobjective lens and the optical disc, but when the light beam, with theradius of curvature R of the wavefront to be detected, is incident onthe focus error detecting circuit provided with predeterminedconditions, the wavefront radius of curvature R can be calculated.

The above-mentioned process can be controlled at a high speed (real timecontrol) since the detecting signal can be obtained by analog form.

The operations described above for the wavefront radius of curvature Rare totally controlled and carried out by the microcomputer 133. First,the microcomputer 133 calculates the beam waist radius W₀ and the beamwaist distance X by the equations 2-3 and 2-4, on the basis of thewavefront radius of curvature R and the projection beam diameter W.Then, the collimating lens 103 is moved by the lens driving mechanism105 and the controller 135, in a manner such that the calculated beamwaist distance X becomes equal to the beam waist distance X inputtedfrom the manual portion 136 or the beam waist distance X having beenstored in the microcomputer 133.

FIG. 62 shows the second embodiment using a radial shearinginterferometer as means for directly detecting the wavefront radius ofcurvature R of means (1). The elements shown in FIG. 59 and having theidentical structure and operations of the first embodiment haveidentical reference numerals and detailed explanation will be omitted.

The structures of the laser light source 101 and rotatable beamprojector 111 are the same as those in the embodiment shown in FIG. 59.The laser beam emitted from the semiconductor laser 102 is, firstly,collimated by the collimating lens 103. Thereafter, a part of thecollimated laser beam is reflected by the PBS 104 towards a firstsemitransparent mirror or half mirror 222 provided in an interferometer221.

Laser beam led to the interferometer 221 by the PBS 104 is incident uponthe half mirror 222 and divided into two beams by the half mirror 222,i.e. a reflecting beam and a passing through beam. The laser beamreflected by the half mirror 222 is used as a beam to be tested whilethe laser beam passed through the half mirror 222 is used as referencebeam.

The laser beam passed through the half mirror 222 is enlarged indiameter by a beam enlarging optical system (i.e. beam expander) 223,and subsequently, the enlarged laser beam is reflected by a first mirror224 and subsequently reflected by a second semitransparent mirror orhalf mirror 226 to thereby reach a CCD camera 228 (i.e. a lightreceiving surface of a CCD image sensor) through a survey lens 227,which forms a reference wavefront on CCD camera 228. It can beunderstood that only a central portion of the laser beam, which can beconsidered to include little wavefront aberration, is enlarged throughthe optical system 223 so as to form this reference wavefront.

On the other hand, the laser beam reflected by the first half mirror 222is incident on a second mirror 225 while maintaining its beam diameter(i.e. maintaining the shape of the wavefront) and is reflected by thesame towards the second half mirror 226. After passing through thesecond half mirror 226, it reaches the CCD camera 228, through a surveylens 227 to form a wavefront to be tested on the CCD camera 228. On thelight receiving surface in the CCD camera 228, the wavefront to betested is consequently superimposed on the reference wavefront. Withthis superimposition, the reference laser beam forming the referencewavefront and the laser beam forming the wavefront to be testedinterferes with each other, and the interference condition thereof ispicked up by the CCD camera 228.

The interference fringes are picked up by the CCD camera 228, and theimage of the interference fringes is changed into digital image signalsto be stored in an image memory 232. The digital image signals are readby a microcomputer 233 from the image memory 232. The microcomputer 233calculates the radius of curvature R of the wavefront in accordance withthe degree of curvature of the interference fringes, and furthercalculates the beam waist distance X and the beam waist diameter W₀through the equations 2-3, 2-4 and displays the calculated results on adisplay 234. The computer 233 actuates the lens driving mechanism 105 tooperate through a controller 235 in accordance with values of thecalculated radius of curvature R of wavefront and the beam waistdistance X, and moves the collimating lens 103 to adjust the distance dbetween the semiconductor laser 102 and the lens 103. With thisadjustment of the collimating lens 103, the beam waist distance X can bekept constant in spite of disturbances, such as temperature change andwavelength change, and also the beam waist position can be shifted to adesired point. The function of an input portion 236 used in thisembodiment is identical with the input portion 136 of the firstembodiment. The laser projecting device of this embodiment may beprovided with the receiving portion 137 and remote controller 141 of thefirst embodiment.

The method for obtaining the radius of curvature R of a wavefront frominterference fringes picked up by the CCD camera 228 will be explainedbelow in detail with reference to FIGS. 63 and 64. (A), (B), (C) of FIG.64 show the. respective interference fringes of the light beams(wavefronts) A, B, C when the radius of curvature R shown in FIG. 63 ofthe light beams A, B, C varies, respectively.

Provided that the number of interference fringes picked-up by the CCDcamera 228 is given as K, the radius of curvature R of the wavefront isobtained by the following formula 2-6. In the conditions shown in FIG.64, the value K can be obtained from the equation: K=ΔP/P.

    R=W.sup.2 /(8λ×K) (R >>W)                     2-6

The value K can easily be determined by a well-known interference fringeanalyzing method, such as, by a phase shifting method. In reality, thereare effects of not only the radius of curvature R of a wavefront butalso wavefront aberration of a higher degree term. However, according tothe above method, not only the radius of curvature R of a wavefront butalso some aberrations can be obtained since the shape of the wavefrontcan be directly detected as the curve of the interference fringes. Bywatching the detected aberrations, an operator can learn whether theperformance of this beam projecting apparatus deteriorates due to somereason. Hence, the condition of operation of this beam projectingapparatus can also be monitored.

When the radius of curvature R of a wavefront has been obtained, thebeam waist distance X and the beam waist diameter W₀ can be gainedthrough the above formulae 2-3 and 2-4.

The third embodiment to which the third aspect of the present inventionis applied will be explained below with reference to FIG. 65. In thisembodiment, a detection system for detecting the radius of curvature Rof a projecting laser beam is adapted for a laser projecting apparatusto project the laser beam, emitted from the laser light source 101, inthree different directions (i.e. horizontal, vertically upward andvertically downward directions). In this embodiment, members havingsimilar structure and operation to those of the embodiments shown inFIGS. 59 and 62 are designated by the same reference numerals and theillustrations of those members will be omitted.

The laser beam projected from the semiconductor laser 102 is collimatedthrough the collimating lens 103 to become a, substantially, parallelbeam. This collimated laser beam is made incident on a beam splitter311. A major part of the collimated laser beam, incident on the beamsplitter 311, is reflected thereby in the direction of the rotatablelaser projector 111 (i.e. in the direction O₂ towards the secondsubject), and the remainder of the collimated laser beam passes throughthe beam splitter 311. In the laser projection apparatus of thisembodiment, the direction O₂ towards the second subject is in the sameplane as the rotational axis 111c. The beam projecting apparatus of thisembodiment is normally installed such that O₂ and rotational axis 111cextend vertically upwards, and a laser beam L₂ projected outwards fromthe apparatus in the direction O₂ functions as a vertically-upwardreference beam.

A part of the laser beam, emitted from the collimating lens 103 andsubsequently passed through the beam splitter 311, then passes through asemitransparent mirror or half mirror 312, and the remainder of thelaser beam is reflected by the half mirror 312 back towards the beamsplitter 311 to be reflected by the same in the direction O₃ towards thethird subject. The laser beam emitted from the beam splitter 311 andpassed through the half mirror 312 is incident on a first focus errordetecting and processing system 321. This first focus error detectingand processing system 321 is equivalent to the combination of theabove-noted focus error detecting system 121 and the controller 131. Thedirection O₃, towards the third subject, extends in the directionopposite to that of O₂, i.e. the beam projecting apparatus of thisembodiment is normally installed such that the direction O₃ extendsdownwards vertically, and a laser beam L₃, projected outwards from theapparatus in the direction O₃, functions as a vertically-downwardreference beam.

The laser beam emitted from the collimating lens 103 and reflected bythe beam splitter 311, in the direction of the rotatable laser projector111, has its diameter enlarged, by a beam expander 313, to apredetermined diameter. The beam expander 313 is of a Gallileo type andincludes a positive lens 315 and a negative lens 314. The negative lens314 is supported so as to be movable, through the lens driving mechanism333, along the optical axis relative to the positive lens 315.

After passing through the beam expander 313, the majority of the laserbeam passes through a half mirror 316 and advances towards the rotatablelaser projector 111, while the remainder is reflected by the half mirror316 towards a second focus error detecting and processing system 331,which is equivalent to the combination of the above-noted focus errordetecting system 121 and the controller 131.

The laser beam emitted from the half mirror 316 towards the rotatablelaser projector 111 is firstly incident upon the half mirror 112. A partof the laser beam incident upon the half mirror 112 passes through thesame to proceed in the direction O₂, while the remainder is reflected bythe half mirror 112 to be subsequently reflected by the mirror 113 inthe direction perpendicular to the rotational axis 111c, i.e. in thedirection O₁ towards the first subject, in a similar manner to that inthe first embodiment to which the third aspect of the present inventionis applied. In general, the rotatable laser projector 111 is rotatedabout the rotational axis 111c while projecting a laser beam L₁ in thedirection O₁, towards the first subject, so as to make ahorizontally-extending reference plane.

The first focus error detecting and processing system 321 mainlymonitors the radius of curvature R of the wavefront of the laser beam L₃projected in the direction O₃ of the third subject, so as to measure theradius of curvature R of the wavefront of the laser beam projected fromthe collimating lens 103. It can be said that the first focus errordetecting and processing system 321 also monitors the major effects onthe radius of curvature of the wavefronts of laser beams L₁, L₂, sincethe first focus error detecting and processing system 321 detects theradius of curvature R of the wavefront of the laser beam emitted fromthe collimating lens 103.

The first focus error detecting and processing system 321 actuates thelens driving mechanism 105, so as to move the collimating lens 103 alongthe optical axis, in accordance with the results of detection, tothereby adjust the radius of curvature R of the wavefront. With thisadjusting operation, the radius of curvature R of the wavefront of eachlaser beam L₁, L₂ or L₃ can be varied so as to shift the beam waistposition.

The second focus error detecting and processing system 331 monitors andmeasures the radius of curvature R of the wavefront of each laser beamL₁, L₂, regardless of the laser beam L₃, and actuates the lens drivingmechanism 33 to move the negative lens 314 along the optical axis,relative to the positive lens 315 to thereby adjust the radius ofcurvature R of the wavefront of each laser beam L₁, L₂ so as to shiftthe beam waist position. With this adjusting operation, the radius ofcurvature R of the wavefront of each laser beam L₁, L₂ can be varied soas to shift the beam waist position.

In this third embodiment, the laser beams L₁ and L₂ projected in thedirections O₁ and O₂ of the first and second subjects, respectively, areliable to be subject to disturbance, e.g. temperature variation, sincethe laser beams L₁ and L₂ are generally projected into the distance, along way away from the beam projecting device. The laser beam L₃ tendsto be subject to little disturbance, since the laser beam L₃ isgenerally projected to a distance far shorter than the above-noted longdistance. Therefore, when the laser beam L₃ is not considered important,the beam waist positions of the laser beams L₁ and L₂ can he adequatelyadjusted through the use of only the second focus error detecting andprocessing system 331 together with the lens driving mechanism 105 or33, without need for the first error detecting and processing system321.

However, the major factor of varying the radius of curvature R ofwavefront of each laser beam L₁, L₂, is a deviation of the distancebetween the collimating lens 103 and the semiconductor laser 102, due toa temperature variation and so forth. Hence, in the case where it isdesired to directly monitor the wavefront of the laser beam emitted fromthe collimating lens 103, or the case where the laser beam L₃ isconsidered equally important as the other two laser beams L₁ and L₂, itis effective that the first error detecting and processing system 321should be used to adjust the beam waist position of each laser beam L₁,L₂, L₃. The beam waist positions of the laser beams L₁, L₂ and L₃ may beadequately adjusted only through the first focus error detecting andprocessing system 321 together with the lens driving mechanism 105,without the second error detecting and processing system 331.

In the above embodiments to which the third aspect of the presentinvention is applied, the knife-edge method or the spot-size method maybe adopted to the focus error detecting system. A lateral-shearinginterferometer may be employed instead of the radial-shearinginterferometer used in the above embodiments. In short, any opticalsystem can be employed if only it has a device for detecting the radiusR of curvature of wavefront of the laser beam emitted by the lightsource.

Although all the embodiments above to which the third aspect of thepresent invention is applied, have been explained under the conditionthat the projecting laser beam is a Gaussian beam satisfying the aboveequations 2-1 to 2-4, in practice, the projecting laser beam isinfluenced by a diaphragm and the like provided in the optical system,which makes the laser beam a non-proportional Gaussian beam.Furthermore, the projecting laser beam is also influenced by aberrationsin the optical system.

Even so, however, if some correction terms are initially added to theequations 2-1 to 2-4, or the data, regarding the beam waist position,the beam waist diameter, etc., is initially obtained with the radius ofcurvature R intentionally changed so as to be stored in a memory, and ifthe microcomputer 133 or 233 operates in accordance with the storeddata, the beam waist position can be adequately corrected. The mostsignificant feature of the beam projecting device, to which the thirdaspect of the present invention is applied, is that the beam projectingdevice is capable of measuring the radius of curvature R of thewavefront by itself.

As can be understood from the foregoing, according to a beam projectingdevice to which the third aspect of the present invention is applied,the beam waist position can be detected and can also be easily adjustedor kept at a predetermined point, thereby making a surveying operationmuch easier.

What is claimed is:
 1. A beam projecting apparatus comprising:a light source emitting a laser beam; a collimating lens for making said laser beam substantially parallel beam; beam protecting means including a beam protecting portion from which said laser beam is projected outwardly so that said laser beam has a beam waist position apart from said beam projecting apparatus; and means for detecting a curvature of wavefront of said parallel beam at predetermined position.
 2. The beam projecting apparatus of claim 1, further comprising beam waist distance calculating means for calculating a distance between said beam waist position and said laser projecting apparatus using a diameter of said beam at said predetermined position and said curvature detecting by said detecting means.
 3. The beam projecting apparatus of claim 2, wherein said detecting means detects a radius of curvature of said wavefront and said beam waist distance calculating means calculates said distance according to the following relationship

    X=R{1+(4λR/πW.sup.2).sup.2 }.sup.-1

wherein "X" represents a distance between said beam waist position and said predetermined position; "R" represents said radius of curvature; "λ" represents a wavelength of said substantially parallel beam; and "W" represents said diameter.
 4. The beam projecting apparatus of claim 1, further comprising waist position controlling means which controls the beam waist position in association with said curvature detected by said detecting means.
 5. The beam projecting apparatus of claim 4, wherein said beam waist position controlling means comprises a collimating lens driving means for driving said collimating lens along an optical axis of said collimating lens for varying said beam waist position.
 6. The beam projecting apparatus of claim 4, wherein said beam projecting apparatus further comprising a beam diameter varying optical system including at least two lens group, and said beam waist position controlling means comprises a lens driving means for driving one of said two lens groups along an optical axis said one of said two lens groups as to vary said beam waist position.
 7. The beam projecting apparatus of claim 1, wherein said detecting means detects said curvature by using astigmatic method.
 8. The beam projecting apparatus of claim 1, wherein said detecting means comprises an interferometer.
 9. A beam projecting apparatus comprising:a light source that emits a light beam; a collimating lens that forms said laser beam into a substantially parallel beam; a beam projecting system including a beam projecting portion from which said laser beam is projected outwardly so that said laser beam has a beam waist position spaced from said beam projecting apparatus; and a detector, said detector detecting a curvature of wavefront of said parallel beam at predetermined position.
 10. The beam projecting apparatus of claim 9, further comprising a beam waist distance calculator that calculates a distance between said beam waist position and said beam projecting apparatus using a diameter of said laser beam at said predetermined position and said curvature detected by said detector.
 11. The beam projecting apparatus of claim 10, wherein said detector detects a radius of curvature of said wavefront and said beam waist distance calculator calculates said distance according to the following relationship:

    X=R{1+(4λR/πW.sup.2).sup.2 }.sup.-1

wherein "X" represents a distance between said beam waist position and said predetermined position; "R" represents the radius of curvature; "λ" represents a wavelength of said substantially parallel beam; and "W" represents the diameter.
 12. The beam projecting apparatus of claim 9, further comprising waist position controller which controls the beam waist position in association with said curvature detected by said detector.
 13. The beam projecting apparatus of claim 12, wherein said beam waist position controller comprises a collimating lens driver that drives said collimating lens along an optical axis of said collimating lens so as to vary said beam waist position.
 14. The beam projecting apparatus of claim 9, further comprising a beam diameter varying optical system including at least two lens groups, and said beam waist position controller comprises a lens driver that drives one of said two lens groups along an optical axis of said one of said two lens groups so as to vary said beam waist position.
 15. The beam projecting apparatus of claim 9, wherein said detector detects said curvature by using an astigmatic method.
 16. The beam projecting apparatus of claim 9, wherein said detector comprises an interferometer. 